Image magnification control device for a camera

ABSTRACT

An image magnification control device for a camera having a photographic lens. A distance &#34;X0&#34; between a rear focal point of said photographic lens and an image taking plane of the camera is detected. Additionally, a defocusing amount &#34;dx&#34; corresponding to a distance between the image taking plane and a surface on which an image is formed by the photographic lens is detected. A magnification ratio γ of a control focal length &#34;f1&#34; required to maintain an image magnification to a present focal length &#34;f0&#34;, that is based on the distance &#34;X0&#34; and the defocus amount &#34;dx&#34; is then calculated in accordance with a predetermined equation. Thereafter, an amount to drive the photographic lens to maintain the image magnification, based on the magnification ratio γ is calculated, and the photographic lens is driven to change a focal length of the photographic lens.

This application is a division of application Ser. No. 08/373,369, filedJan. 17, 1995, now U.S. Pat. No. 5,541,702, which is a division ofapplication Ser. No. 08/149,226, filed Nov. 2, 1993, which issued asU.S. Pat. No. 5,428,419 on Jun. 27, 1995, which is a continuation ofapplication Ser. No. 07/881,785, filed May 11, 1992, which issued asU.S. Pat. No. 5,283,607 on Feb. 1, 1994, which is a continuation ofapplication Ser. No. 07/652,038, filed Feb. 4, 1991, which issued asU.S. Pat. No. 5,159,377 on Oct. 27, 1992, which is a continuation ofapplication Ser. No. 07/410,880, filed Sep. 22, 1989, which issued asU.S. Pat. No. 5,093,680 on Mar. 3, 1992.

BACKGROUND OF THE INVENTION

This invention relates to an image magnification control device for acamera, wherein a photographic lens for a camera, including single lensreflex cameras and video still cameras, is driven and controlled by azoom drive means so as to automatically control an image magnificationof the photographic lens to a predetermined magnification.

A desirable feature for a power zoom camera is to be able to maintain aconstant image magnification of an object as the distance between theobject and the camera varies. For instance, when taking a series ofcontinuous photographs, of for instance, a baseball player running tocatch a ball, the photographer may wish that the baseball playeroccupies the same area of the film frame as the player moves. This canbe accomplished by varying the focal length of the lens as the playermoves. Unfortunately, an individual cannot change the magnificationvalue (by changing the focal length of the lens) fast enough andaccurately enough to achieve the desired result.

Over the years, camera manufacturers have developed power zoom lensesfor lens shutter cameras. This enables a photographer to quickly andsmoothly change the focal length of the camera lens. Lens shuttercameras typically employ a triangulation technique to determine thedistance of an object to be photographed from the camera. In thetriangulation technique, a source of light, such as infrared orultrasonic, is emitted by the camera. The light source is bounced off ofan object to be photographed and returned to the camera. By utilizingthe triangulation technique, the distance "a" of the object can bedetermined.

The magnification value of a lens shutter camera is determined by anequation m=f/a, where "m" equals the magnification value, "f" equals thefocal length of the lens and "a" equals the distance of the object fromthe camera. If a constant picture image size is to be maintained, thelens shutter camera must merely determine the distance of the objectfrom the camera and change the focal length of the lens according to theabove equation, so that the magnification value, "m", remains constant.This is easily accomplished with a power zoom, auto-focus, lens shuttercamera.

Many individuals prefer using interchangeable lens cameras, such as SLRcameras, because a plurality of different lenses can be easily attachedto a camera body. It would be desirable to enable an interchangeablelens camera to also be able to maintain the constant picture image sizeas the object to be photographed moves relative to the camera. However,constant image magnification techniques that are applicable to lensshutter cameras are not applicable to interchangeable lens cameras.

In an interchangeable lens camera, triangulation techniques aregenerally not used for focusing purposes because of inherentinaccuracies in such a system. Such inaccuracies are acceptable when asmall size lens (i.e., 70 mm) is used, but is unacceptable when a largesize lens (i.e., 200 mm) is employed. Due to the intrinsic errors of thetriangulation technique, manufacturers developed a technique forfocusing an object based on the amount of defocus of the object to bephotographed. Two such defocus techniques are a phase differencedetection (PDD) method and a contrast difference (CD) method.

A camera employing the defocus technique for focusing does not determinethe distance "a" of an object from the camera. Thus, it is not possibleto maintain a constant image magnification value "m" as the distance "a"of the object changes, using the techniques developed for lens shuttercameras (i.e., m=f/a). Because it is desired that the typicalinterchangeable lens camera be able to maintain a constant imagemagnification value as the distance of an object to be photographed fromthe camera moves, an alternative system must be developed.

Two methods exist for making an image on a film frame occupy the sameamount of space, even though the distance between the object to bephotographed and the camera varies. In the first method, thephotographer preliminarily sets the size of the image before taking apicture. For instance, the photographer can select a portrait mode ofoperation, after which all pictures that are taken will be of theportrait type. In the second method, the camera photographer views thesize of the image (as shown in the viewfinder) and adjusts the focallength of the lens until he likes the size. Then, the operator "fixes"the size. Thereafter, even if the object moves or the lens zooms, theimage size of the object will be fixed. The present invention embodiesboth methods for making the image constant.

An image magnification control device for a camera, using a linkingmechanism for a zoom lens device is disclosed, for example, in JapanesePatent Publication No. SHO 60-1602. In this prior art, a cam mechanismprovided in a zoom lens controls the amount of zooming of the zoom lensso as to keep the ratio of a real subject length and a real focal lengthconstant. Moreover, in this cam mechanism, a cam surface provided in alens barrel is formed in a shape of a logarithmic curve. By touching alinked roller which travels in the forward and backward directions inparallel with the lens axis to the cam surface using aspiring, as thelens barrel rotates, the linked roller follows the cam surface. Inaddition, a variable resistor is linked with the linked roller so as tocontrol the amount of zooming by means of such a variable resistor.

However, it is preferred that the position where the linked rollertouches the cam surface be at the intersection of a plane including thecenter line of the linked roller and the lens axis and of the camsurface.

However, there is a limit to how much one can decrease the radius of thelinked roller. Since the cam surface is in the shape of a logarithmiccurve, rather than a linear shape, the position where the linked rollertouches the cam surface deviates from the intersection described abovedue to a change of slope of the cam surface. Thus, there is a tendencyfor the amount of deviation to depend on the degree of the slope of thecam surface. Such a deviation is undesirable for a precise zoomingcontrol.

In addition, it is very difficult to accurately machine a cam surface,with a high precision, in the shape of a logarithmic curve.

Further, a camera which is equipped with a CPU used for conducting anautofocus control and process control has been developed. For such acamera, motors therein may drive a zoom lens and conduct the imagemagnification.

When a release process is performed while a subject is out of the rangewhere the image magnification can be controlled, a photograph is takenin the condition where a predetermined image magnification is notobtained, resulting in an undesirable situation.

In this case, when a subject moves out of a range where the imagemagnification can be controlled, the image magnification control istemporarily stopped. When the subject moves back too many spaces intothe allowable range of the image magnification control, it is desirableto resume the image magnification control. In addition, it is preferredthat this operation be conducted simply.

Moreover, there has been a camera which is equipped with aninterchangeable lens. For such a camera, motors therein may drive a zoomlens and conduct the image magnification.

In the meantime, when such an image magnification control is performedin a sequence shot mode, if a subject moves after it has been focusedand until the next release process is conducted, the next photographwould be unfocused.

Further, new types of electronically controlled cameras have beendeveloped having features, such as autofocus control and programcontrol. Conventionally, a camera has been known wherein a focus locktakes place when a subject is focused and a light metering operation isstarted by turning ON a light metering switch in an auto and in-focuspriority mode. As another prior art camera, a camera has been devisedwherein pressing an image magnification mode setting switch allows anautofocus operation and power zoom operation to take place regardless ofthe distance to a subject so as to automatically control an imagemagnification of a photographic lens. By combining the functions of theabove cameras, the performance of such cameras can be enhanced.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide atechnique for maintaining a constant image magnification value of anobject that moves relative to the camera, by varying the focal length ofthe lens secured to the camera.

An advantage of the present invention is its applicability to all typesof cameras, such as lens shutter cameras, SLR cameras, electronic videocameras and electronic still cameras.

Another advantage of the present invention is the ability to provide animage magnification control device which can automatically control animage magnification to a predetermined value without using a cammechanism.

Another object of the present invention is to provide an imagemagnification control device which prohibits a user from taking aphotograph when a subject is not in the allowable range of the imagemagnification control, until the subject is in the allowable range so asto prevent wasteful photographs.

A further object of the present invention is to provide an imagemagnification control device for interchangeable lens cameras which caneasily set an image magnification from the outside.

A further object of the present invention is to provide an imagemagnification control device for a camera wherein after a subject isfocused and a shutter is released in the sequence shot mode, the subjectis focused again, so that in-focus photographs can be taken even if thesubject, which has been previously focused, moves between shutterrelease operations.

Another object of the present invention is to provide an imagemagnification control device for a camera which satisfies both the focuslock function and image magnification function in the manner that whenthe image magnification control signal is output from the imagemagnification setting means in the in-focus priority mode of thepriority mode selection switch, the light metering switch is turned ONand a subject is focused, so that the image magnification control takesplace rather than the focus lock.

For the above purposes, according to the present invention, there isprovided an image magnification control device for a camera, whichcontrols the image magnification to be a set magnification, comprising:

means for detecting defocus information by analyzing a light that passedthrough the photographic lens;

means for computing a control focal length, which is required tomaintain the image magnification at the set magnification, based uponthe defocus information detected by the detection means; and

means for controlling a focal length of the photograph lens in responseto the computation means so as to maintain a constant imagemagnification.

Optionally, the image magnification setting means may comprise anexternal setting means to set the image magnification from outside thecamera.

According to another aspect of the invention, there is provided an imagemagnification control device for a camera, comprising:

means for detecting a distance "X₀ " between a rear focal point of aphotographic lens and an in-focus position of the photographic lens froma delivery-amount of a focusing lens;

means for detecting defocus information "dx" of the photographic lens byanalyzing light that passed through the photographic lens;

means for detecting a focal length "f₀ " of the photographic lens;

means for setting an image magnification "m₀ " for taking a photograph;

means for computing a control focal length "f₁ " in accordance with anequation: ##EQU1## using said x₀, dx, f₀ and m₀ ; and means forcontrolling the focal length of the photographic lens so as to meet thecontrol focal length.

In another aspect of the invention, there is provided an imagemagnification control device for a camera comprising:

means for setting an image magnification to a certain magnification;

means for detecting a focal length of a photographic lens;

means for controlling the focal length of the photographic lens so as tomaintain the image magnification set by the image magnification settingmeans; and

means for determining whether the set image magnification is in acontrollable range with the present focal length detected by thedetecting means.

Optionally, the above device further comprises means for inhibiting ashutter-release operation until the focal length comes into a rangewherein the set image magnification can be obtained when it isdetermined by the determining means that the image magnification is outof the controllable range.

Also optionally, the above device further comprises means for inhibitingthe image magnification control by disabling the focal length controlmeans until the focal length comes into a range wherein the set imagemagnification can be obtained, when it is determined by the determiningmeans that the image magnification is out of the controllable range.

Moreover, the above device may optionally comprise means for indicatinga warning, when it is determined by the determining means that the imagemagnification is out of the controllable range.

According to another aspect of the invention, there is provided an imagemagnification control device for a camera, comprising:

means for driving a photographic lens for focusing;

means for driving the photographic lens for zooming;

means for setting an image magnification to a certain magnification;

means for detecting a focal length of the photographic lens;

means for determining whether the image magnification set by the imagemagnification setting means is in a controllable range with the presentfocal length detected by the detection means; and

means for controlling the zoom driving means to maintain the imagemagnification set by the image magnification setting means, wherein thecontrol means disables at least the zoom driving means or the focusdriving means when it is determined by the determining means that theimage magnification is out of the controllable range until it isdetermined by the determining means that the focal length comes backinto a range wherein the set image magnification can be obtained.

In still a further aspect of the invention, there is provided an imagemagnification control device for a camera wherein either a single-shotphotographing mode or a sequential-shot photographing mode can beselected, comprising:

means for setting an image magnification to a certain magnification; and

means for controlling a photographic lens so as to maintain the imagemagnification set by the image magnification setting means, wherein thecontrol means drives the photographic lens, in the case where thesequential-shot mode is selected, in such a fashion that once a subjectis focused at the image magnification set by the image magnificationsetting means in the sequential-shot photographing mode, the focusingoperation is sequentially performed at the set image magnification asthe subject moves.

Other aspects of the invention provide an image magnification controldevice for a camera wherein either a focus-priority mode or ashutter-release-priority mode can be selected, comprising:

means for setting an image magnification to a certain magnification; and

means for controlling a photographic lens so as to maintain the imagemagnification set by the image magnification setting means, wherein thecontrol means executes a focus-lock operation when a subject is focusedin the focus-priority mode while the image magnification has not beenset, and the control means executes the image magnification controlwithout executing the focus-lock operation when a subject is focused inthe focus-priority mode while the image magnification has been set bythe image magnification setting means.

DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1 is a control block circuit diagram of an image magnificationcontrol device of a camera in accordance with the present invention;

FIG. 2 is a detail circuit diagram of the image magnification controldevice in a camera body of the camera shown in FIG. 1;

FIG. 3 is a detail circuit diagram of the image magnification controldevice in a photographic lens of the camera shown in FIG. 1;

FIG. 3(a) is a modification of FIG. 3;

FIG. 4 is an outlined descriptive diagram showing a part of the drivingmechanism of the zooming lens group of the photographic lens shown inFIG. 1;

FIG. 5 is a descriptive diagram of a zoom code plate shown in FIG. 4;

FIG. 6 is an outlined descriptive diagram showing the relationshipbetween a subject and image taken by the photographic lens;

FIGS. 7a, and 7c are outlined descriptive diagrams which describe theimage magnification constant theory in accordance with the presentinvention;

FIG. 8(a) is a three-dimensional change coordinate diagram showing achange of the focal point of a focusing lens group by a zoom operation;

FIG. 8(b) is a descriptive diagram which describes the meaning of thecoordinates shown in FIG. 8(a);

FIG. 9(a) is a three-dimensional change coordinate diagram showing achange of the amount of defocusing of the focusing lens group by a zoomoperation;

FIG. 9(b) is a descriptive diagram which describes the meaning of thecoordinates shown in FIG. 9(a);

FIG. 10 is a descriptive diagram showing the relationship between a zoomposition and K value of the zooming lens group;

FIG. 11 is a descriptive diagram showing the relationship between a zoomposition of a zooming lens group and the focal length of the focusinglens group;

FIG. 12 is a descriptive diagram of a compensation curve where therelationship between the zoom position and K value of the zooming lensgroup shown in FIG. 10 is compensated;

FIG. 13 is a descriptive diagram of a compensation curve where therelationship between the zoom position of the zooming lens group and thefocal length of the focusing lens group shown in FIG. 11 is compensated;

FIGS. 14 to 42 are flow charts describing the operations of the imagemagnification control device of the camera in accordance with thepresent invention;

FIGS. 14(a), 15(a), 15(b) and 17(a) are modifications of FIGS. 14, 15and 17, respectively;

FIG. 43 is a descriptive diagram showing another example of the zoomposition detection means for detecting a zoom position of the zoominglens group;

FIG. 44 is an exploded diagram of the reflection plate shown in FIG. 43;

FIG. 45 is a descriptive diagram showing another example of the zoomposition detection means for detecting a zoom position of the zoominglens group;

FIG. 46 is a descriptive diagram of an electrode plate shown in FIG. 45;

FIG. 47 is a descriptive diagram of another example of the zoom positiondetection means for detecting a zoom position of the zooming lens group;

FIG. 48 is a descriptive diagram which conceptually shows an example ofthe power zoom mechanism of the photographic lens;

FIG. 49 is a front view of a slit plate shown in FIG. 48;

FIG. 50 is a front view of another example of a PZ pulser shown in FIG.48;

FIG. 51 is a descriptive diagram of a reflection plate shown in FIG. 50;

FIG. 52 is a descriptive diagram showing another example of the PZpulser shown in FIG. 48; and

FIG. 53 is a front view of a multiple side reflector shown in FIG. 52.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1 illustrates an outlined descriptive diagram of a camera which isprovided with a function which keeps an image magnification constantregardless of whether a subject moves. The camera comprises a cameramain unit 1, a lens mount 2 that is part of the camera main unit 1, anda photographic lens 3 that is interchangeably mounted on the lens mount2. The photographic lens 3 is provided with an autofocus mechanism (AFmechanism), comprising a focus drive means and a power zoom mechanism(PZ mechanism) comprising a zoom drive mechanism. In the embodiments, AFand PZ refer to autofocus and power zoom, respectively.

A zoom lens can be constructed in many ways. Two types of zoom lensesare commonly employed in cameras. The first commonly employed type ofzoom lens is referred to as a so-called zoom lens. The second type ofcommonly employed zoom lens is referred to as a vari-focal lens. It isunderstood that the present invention is not limited to any particularzoom lens construction.

In a so-called zoom lens, light rays that pass through the lens arealways projected to a fixed point, such as the film image plane,regardless of the setting of the focal length of the lens. In avari-focal zoom lens, light rays that pass through the lens are notalways projected to a fixed point. That is, the vari-focal lens has thedisadvantage that as the focal length of the lens changes, the lightrays that pass through the lens falls either in front of or behind thefilm image plane. Thus, it is necessary to compensate for thepositioning of the focusing lens elements so that the light rays willfall onto the film image plane.

The camera main unit 1 includes a camera control circuit 4, which ismore clearly shown in FIG. 2. The photographic lens includes a lenscontrol circuit 5, which is more clearly shown in FIG. 3.

Camera Control Circuit

The camera control circuit 4 comprises a main CPU 6 and a display CPU 7.A serial input terminal SI of the main CPU 6 is connected to a serialoutput terminal SO of the display CPU 7; a clock terminal SCK of themain CPU 6 is connected to a clock terminal SCK of the display CPU 7.

Terminal PF of the main CPU 6 is connected to a DX circuit 8 fordetecting an ISO sensitivity of a film (i.e., a DX code). Terminal P20of the main CPU 6 is connected to a switch, SWAF A/M, for selecting anautomatic operating mode or a manual operating mode of the camera mainunit 1. Terminal 21 of the main CPU 6 is connected to a switch, SWAFS/C, which selects an in-focus priority mode or a release priority modeof operation.

The DX circuit 8 and switches SWAF A/M and SWAF S/C are connected to aground wire 9. Terminals P2 to P9 of the display CPU 7 are selectivelyconnected to the ground wire 9 through a switch group SW-I, whichincludes a light metering switch SWS, a release switch SWR, a powerON/OFF lock switch SWLOCK, a mode switch SWMODE, a drive switch SWDRIVE,an exposure compensation switch SWXV, an up switch SWUP, and a downswitch SWDOWN. By operating the mode switch SWMODE, along with the upand down switches SWUP and SWDOWN, a program photograph mode, anautomatic photograph mode, a manual photograph mode, and so forth can beselected. In addition, by operating the up and down switches SWUP andSWDOWN along with the drive switch SWDRIVE, a sequence shot (i.e.,sequential photography) mode, a single shot (i.e., single photograph)mode, a self-timer mode, and so forth can be selected. Moreover, byoperating the up and down switches SWUP and SWDOWN along with theexposure compensation switch SWXV, an exposure value can be compensated.The light metering switch SWS and release switch SWR are actually asingle push button that activates a light meter when the switch isdepressed halfway and releases the shutter when the switch is fullydepressed.

The main CPU 6 includes terminals PA, PB, PC, PD, PE, VDD, and Gnd. Alight reception element 10, such as a LED, is used to measure theluminance of a subject that is seen by the photographic lens 3. Thelight reception element 10 is interfaced to an A/D circuit 11, which isthen inputted to terminal PA. An exposure compensation signal isoutputted from terminal PB to an exposure control circuit 12. TerminalPC is connected to a charge-coupled device (CCD) 14 for AF, namely,in-focus operation, as a defocusing amount detection means through a CCDprocess circuit 13. The CCD 14 receives a light beam that is bounced offthe subject and enters the photographic lens 3, so as to detect a focalpoint. A motor control signal is inputted from terminal PD to an AFmotor control circuit 15. The AF motor control circuit 15 drives andcontrols an AF motor 16 located in the camera main unit 1.

The AF motor 16 rotates a coupler 18 (FIG. 1) through a speed reductiongear 17. When the photographic lens 3 is mounted on the lens mount 2,the coupler 18 may engage a lens side coupler (which is linked to afocusing lens group at the end of the lens barrel), causing the AF motor16 to be linked with the focusing lens group of the photographic lens 3,so that the focusing lens group can be focused by the AF motor 16.However, a lens corresponding to this embodiment does not have toprovide a lens side coupler which is engaged with the coupler 18. Insuch a case, the AF motor 16 does not drive the focusing lens group. Inaddition, the speed reduction gear 17 is linked with an AF pulser 19,the output of the pulser 19 being inputted to terminal PE of the mainCPU 6.

Terminal P_(SEG) on the display CPU 7 is interfaced to a LCD display 20.Terminals P10 to P17 of the display CPU 7 are connected to informationtransfer connection terminals Fmax1 to Fmax3, Fmin1 and Fmin2,auto/manual information connection terminal A/M-T, common connectionterminal Cont, and power connection terminal Vdd-T, respectively. AnON/OFF signal is inputted from terminal P18 of the display CPU 7 to aswitch circuit 21, which is also connected to a power connectionterminal VBatt.

The positive side of battery 22 is connected through a regulator 23 toVdd1 of the display CPU 7 and a capacitor 24. The positive side of thebattery 22 is also connected to power terminal VDD of the main CPU 6through DC/DC converter 6', and to the switch circuit 21. An ON/OFFcontrol signal is outputted from terminal P1 of the display CPU 7 andinputted to the DC/DC converter 6'.

The negative side of the battery 22 is connected to ground terminal Gndof the main CPU 6, ground terminal Gnd of the display CPU 7, the groundwire 9 of the operation switch group SW-I, and a ground connectionterminal Gnd-T.

The connection terminals Fmax1 to Fmax3, Fmin1, Fmin2, Cont, Vdd-T,VBatt, and Gnd-T are provided at the end of the lens mount 2. They forma connection terminal group T-I of the camera body.

When the main switch, namely, the lock switch SWLOCK is in the OFFposition, an operation signal is not outputted from terminal P1 of thedisplay CPU 7 to the DC/DC converter 6'. Thus, no power is supplied fromthe battery 22 to the main CPU 6, and the main CPU 6 is in the OFFstate.

On the other hand, the battery voltage is applied to terminal VDD of thedisplay CPU 7 through regulator 23, so that the display CPU 7 operateseven if the lock switch SWLOCK is in the OFF position. In this state,the LCD display 20 is OFF.

When the lock switch SWLOCK is turned ON, an ON signal is inputted toterminal P4 of the display CPU 7. A display signal is outputted fromterminal P_(SEG) of the display CPU 7 to the LCD display 20, and the LCDdisplay 20 lights. At that time, an operation signal is outputted fromterminal P1 of the display CPU 7 to the DC/DC converter 6' and thevoltage of the battery 22 is applied to terminal VDD of the main CPU 6,activating the main CPU 6.

Power Zoom Focus Structure of Photographic Lens

The photographic lens 3 (FIG. 4) provides a power zoom mechanism whichdrives zooming lens groups 25 and 26 and a focus drive mechanism whichdrives a focus lens (not shown).

The power zoom mechanism has a ring-shaped fixing frame 27, a lens frame28 which is engaged with the fixing frame 27 in a manner that the lensframe 28 can travel in an axial direction therein, a first cam ring 29which is engaged with the fixing frame 27 in the manner that the firstcam ring 29 can freely rotate on the outer surface of the fixing frame,a second cam ring 30 which is engaged with the first cam ring 29 in themanner that the second cam ring 30 can freely rotate on the outersurface thereof and can freely travel in the axial direction, and a lensframe 31 fixed to the cam ring 30. The lens frames 28 and 31 mount thelens groups 25 and 26, respectively.

Located on the fixing frame 27 is a guide hole 32 which is parallel withthe axial line. Located on the cam ring 29 are slit cams 33 and 34. Aslit cam 35 and a guide hole 36 are on the cam ring 30, which areparallel with the axial line. A guide roller 37, mounted on the outersurface of the lens frame 28, is inserted and engaged with the guidehole 32 and slit cam 33. A guide roller 38, mounted on the peripheral ofthe fixing frame 27, is inserted and engaged with the slit cam 34 andguide hole 36. A guide roller 39, mounted on the outer surface of thecam ring 29, is inserted and engaged with the slit cam 35.

The above focus drive mechanism has an AF motor M1 which drives thefocus lens group (not shown) and a PZ motor M2 which drives the cam ring29 (see FIG. 1). A variable aperture stop (not shown) provided in anoptical path of the photographic lens 3 is controlled by an AE motor M3.The motor M1 and focus lens group, and the motor M2 and zoom lens groupare linked through a friction type clutch.

Between a base of the cam ring 29 and a code plate mounting member (notshown), located on the fixing frame 27, is a zoom position reading meansthat is provided as a focal length detection means. The zoom positionreading means has a zoom code plate 40 (FIGS. 4, 5) which is supportedwith a cord plate supporting member which is located concentric with thecam ring 29 and a brush 41, which elastically touches the inner surfaceof the zoom code plate. In addition, on the inner surface of the zoomcode plate 40 are a plurality of pattern contacts which areintermittently provided in the peripheral direction. The patter contactsand brush 41 work together, outputting a zoom position signal.

On the focus lens side of the lens 3 is a focus position reading means(namely, a distance reading means (not shown)) which is provided as afocus position detection means. The distance reading means uses the samestructure as the zoom position reading means. A distance signal isobtained from a distance code plate 42 (refer to FIGS. 1 and 3) which issimilar to the zoom code plate 40.

Lens Control Circuit

Referring to FIG. 3, an end surface of the photographic lens 3, which isconnected to the lens mount 2, contains a plurality of connectionterminals Fmax1' to Fmax3', Fmin1', Fmin2', Cont', Vdd-T', VBatt', andGnd-T'. When the photographic lens 3 is mounted on the lens mount 2 ofthe camera body 1, connection terminals Fmax1' to Fmax3', Fmin1',Fmin2', Cont', Vdd-T', VBatt', and Gnd-T' of the lens 3, which form aconnection terminal group T-II, are connected to connection terminalsFmax1 to Fmax3, Fmin1, Fmin2, Cont, Vdd-T, VBatt, and Gnd-T,respectively. The connection terminal groups T-II and T-I form aconnection section TC. Data is transferred between the camera controlcircuit 4 and the lens control circuit through the connection sectionTC.

The photographic lens 3 is equipped with a lens ROM 43 which storesinformation intrinsic to a lens, and a lens CPU 44 which controls thelens and performs other operations. The information intrinsic to thelens includes the number of pulses for maximally advancing the focuslens group and zoom lens group, availability of power zooming,availability of power focusing, presence of variable focus lens, andfocus compensation value by zooming operation. An output signal of thezoom code plate 40 is inputted to terminal PL of the lens ROM 43 andterminal PK of the lens CPU 44. A distance signal from the distance codeplate 42 is inputted to terminal PM of the lens ROM 43.

Motor control signals, which are outputted from terminals PH, PI, and PJof the lens CPU 44, are inputted to an AF motor drive section (AF motorcontrol circuit) 45, PZ motor drive section (PZ motor control circuit)46, and AE motor drive section (AE motor control circuit) 47,respectively. The motor drive sections 45, 46, and 47 control motors M1,M2, and M3, respectively. The rotations of the motors M1, M2, and M3 aredetected by an AF pulser 48 (a focus position detection means), PZpulser 49 (zoom position detection means, namely, a focal lengthdetection means), and AE pulser 50. Output signals of the pulsers 48,49, and 50 are inputted to terminals P20 to P22 of the lens CPU 44.

Connection terminal VBatt' is connected to power input sections of themotor drive sections 45 to 47. Connection terminal Vdd-T' is connectedto power terminal Vdd of the lens CPU 44 and to one end of a resistor 51and the cathode of a diode 52. The other end of the resistor 51 andanode of the diode 52 are connected to a reset terminal RESET of thelens CPU 44 and to one end of a capacitor 54, while the remaining end ofthe capacitor is connected to a ground wire 53. The ground wire 53 isconnected to connection terminal Gnd-T', ground terminal Gnd of the lensROM 43, and ground terminal Gnd of the lens CPU 44. In addition, theground wire 53 is connected to auto/manual selection switch SWAF(A/M),power zoom mode switch SWPZ (A/M), image magnification constant modeswitch SWPZC (which keeps an image magnification of the zoom lensconstant), zoom switch SWPZT (which drives the zoom lens to a Teleterminus (telephoto terminus) side), and zoom switch SWPZW (which drivesthe zoom lens in a Wide terminus (wide-angle terminus) side). Theremaining terminal of the switches SWAF(A/M), SWPZ(A/M), SWPZC, SWPZT,and SWPZW are connected to terminals P23 to P27 of the CPU 44.

Connection terminal Fmax1' is connected to reset terminal RESET of thelens ROM 43, interrupt terminal Int of the lens CPU 44, and an emitterof transistor 55. Connection terminal Fmax2' is connected to a clockterminal SCK of the lens ROM 43, clock terminal SCK of the lens CPU 44,and an emitter of transistor 56. Connection terminal Fmax3' is connectedto a serial output terminal SO of the lens ROM 43, serial input/outputterminal SI/SO of the lens CPU 44, and an emitter of transistor 57.Connection terminal Fmin1' is connected to terminal RDY (not RDY) of thelens CPU 44 and an emitter of transistor 58. Connection terminal Fmin2'is connected to ground wire 53 through a fuse 59 for settinginformation. Connection terminal A/M-T' is connected to ground wire 53through switch SW A/M, which selects an automatic mode (or program mode)and a manual mode which is operated by an aperture ring. Connectionterminal Cont' and the bases of transistors 55 to 58 are connected topower input terminal Vcc of the lens ROM 43. The collectors of thetransistors 55 to 58 are connected to the ground wire 53.

Theory of Constant Image Magnification

Referring to FIG. 6, F₁ represents a focal position on a front side(substance side, namely subject side), F₂ represents a focal position ona rear side (image side) of the photographic lens, y₁ represents a sizeof the substance (subject) on the front side of the photographic lens 3,y₂ represents the size of the image focused on the rear side of thephotographic lens 3 by rays of light from an infinitive position, arepresents a distance from the front focal position F₁ to the image; xrepresents a distance from the rear focal point F₂ to the substance; andf represents a focal length of the photographic lens 3. The position atwhich an image y₂ is formed becomes a focused position.

An equation for the image formation shown in FIG. 6 is given as follows:

    a*x=f.sup.2                                                A

    m=y.sub.2 /y.sub.1 =(x+f)/(a+f)                            B

Based on the distance a of the subject, the image magnification m can beobtained using equations A and B above:

    m=f/a                                                      (1)

On the other hand, based on the distance x on the image side, the imagemagnification m can be obtained using equations A and B:

    m=x/f                                                      (2)

Assuming that the image magnification is m₀ when x and f in equation (2)is x₀ and f₀, respectively, as shown in FIG. 7(a), the imagemagnification m₀ is given as follows:

    m=x.sub.0 /f.sub.0                                         (3)

Assuming that the distance from the front focal position F₁ to thesubstance (subject) y₁ is a₁ when a defocus dx occurs, as shown in FIG.7(b), as the substance y₁ moves, equation A becomes:

    a.sub.1 (x.sub.0 +dx)=f.sub.0.sup.2                        (4)

Distance a₁ can be rewritten using equation (4), as follows:

    a=f.sub.0.sup.2 /(x.sub.0 +dx)                             (5)

Assuming that a new focal length is f, so as to keep the imagemagnification constant (m₀ : constant), equation (1) can be described asfollows:

    m.sub.0 =f/a.sub.1                                         (6)

Rewriting the equation for obtaining the focal length f and substitutingequations (3) and (5) into the equation, yields: ##EQU2## With equation(7) a zoom ratio f/f₀ is obtained as follows: ##EQU3##

Thus, by driving the zoom ring in accordance with the zoom ratio, theimage magnification becomes constant (m₀ =f/a₁ =x₀ /f₀), as shown inFIG. 7(c).

The focal length of the photographic lens 3 changes depending on thezoom position and focus position in three dimensions on a focal pointcurved surface 60, as shown in FIG. 8. Consequently, the distance x₀from the focal length to the image also changes depending on the zoomposition and focal position in three dimensions on a surface 61, asshown in FIG. 9.

Moreover, a K value Kval (which is the deviation between the amount oflens advancement and the focal point) changes depending on the zoomposition of the photographic lens 3. The relationship between the zoomposition and Kval, as represented by the zoom code plate 40 stepwisechanging along a compensation coefficient line 62, is illustrated by asolid line in FIG. 10. In addition, the relationship between the zoomposition and focal length also stepwise changes along a compensationcoefficient line 63, as shown in FIG. 11. In the cases of FIGS. 10 and11, it is desirable that the compensation coefficient lines 62 and 63for the zoom control and focus control smoothly change, as illustratedby broken lines 62' and 63', respectively. To accomplish this,compensation information, listed in Table 1, is stored in the lens ROM43 and f and x₀ are computed by the lens CPU 44.

Table 1 Compensation Information

01 Number of initial pulses in encoder of zoom code plate P_(h)

02 Width of initial pulses in encoder of zoom code plate P_(h)

03 Initial Kval K_(h)

04 Compensation coefficient of initial Kval K_(c)

05 Initial focal length f_(h)

06 Compensation coefficient of initial focal length f_(h)

07 Primary compensation coefficient of focus lens position and focallength f_(fc1)

08 Secondary compensation coefficient of focus lens position and focallength f_(fc2)

09 Coefficient for computing amount of advancing x₀, Q, R, S, and T,

10 Conversion coefficient from image magnification to zoom drivingpulsers A, B, and C

The start Kval, (start K value represents a Kval of the left and rightmost ends of step K_(i)) (where i=0, 1, 2, 3, . . . ) of thecompensation coefficient 62 is shown in FIG. 10. In other words, whenthe lens moves from the L (Tele) side to the S (Wide) side, the rightend of the step K_(i) is Kval. Conversely, when the lens moves from theS (wide) side to the L (Tele) side, the left end of the step K_(i) isKval.

The compensation coefficient of initial Kval K_(c) is a coefficient forapproximately computing a value that corresponds to the curve 62' as aslope of a straight line at the step K_(i). The initial focal lengthf_(h) refers to one of the left and right ends of the compensationcoefficient line f_(i) (where i=0, 1, 2, 3 . . . N) like the initialKval. The compensation coefficient of initial focal point f_(c) is acoefficient for approximately computing a value corresponding to thecompensation curve 63' as a slope of a straight line at the step f_(i).The Kval and focal length obtained in this manner are illustrated ascompensation curves 62" and 63", shown in FIGS. 12 and 13, respectively.The primary compensation coefficient of the focus lens position andfocal length f_(fc1) can be obtained from a curve 64 determined by thezoom position and focal length shown in FIG. 8. The secondarycompensation coefficient of focus lens position and focal length f_(fc2)is determined by the three dimensional focal point curved surface 60,where the focus amount is considered against f_(fc1) described above.

The focal point curved surface 60 is a curved surface which isdetermined by optical designing and mechanical designing of thephotographic lens 3. It cannot be accurately and proportionallyrepresented with a simple equation. The amount of advancing the focuslens defined by such a curved surface is relatively proportional to theamount of zooming of the zoom lens. Thus, it is necessary to compensatethe amount of advancing of the focus lens. The compensation coefficientsfor that are Q, R, S, and T, which depend on the optical designing andmechanical designing of the lens. Moreover, equation (10), which usesthe compensation coefficients Q, R, S, and T, depends on the opticaldesigning and mechanical designing of the photographic lens. The numberof pulses for diving the zoom lens, P_(z), which is used to keep theimage magnification constant, depends on the optical designing andmechanical designing of the photographic lens. Thus, the compensationcoefficients A, B, and C of equation (11), which computes Pz, also aredetermined by the optical designing and mechanical designing.

Assuming that the number of pulses at the absolute position of thepresent zoom ring of the photographic lens 3 is P_(s) and that thepresent focus lens is P_(inf), the focal length f and the amount ofadvancing x₀ are obtained as follows: ##EQU4## In this case, consideringan over-moving of the amount of advancing of the lens on the infiniteside, P_(inf) should be a small value. In addition, assuming that thecontrol image magnification is γ, the number of zoom driving pulsesP_(z) can be obtained from the following equation:

    P.sub.z =Aγ.sup.3 +Bγ.sup.2 +Cγ          (11)

The data listed in Table 1 and the computation equations described arestored in advance in the lens ROM 43 of the photographic lens 3.

Major terms used in the flow charts, which represent control operationsof the camera control device structured as above, are described asfollows:

AFSTOP represents a process which stops the focusing lens group;

FL stands for the far limit and is a flag for representing whether thefar terminus of the focusing lens group is being detected. When FL=1,the control circuit detects that, the focusing lens group is positionedat the far terminus;

NL stands for the near limit and is a flag for representing whether thenear terminus of the focusing lens group is being detected. When NL=1,the control circuit detects that the focusing lens group is positionedat the near terminus;

P_(inf) represents the number of pulses where the focusing lens group isdriven from the far terminus to the near terminus. When P_(inf) =0, thefocusing lens group is positioned at the far terminus. The number ofpulses is detected by the AF pulser 48;

WL stands for the wide limit and is a flag for representing whether thewide terminus of the zooming lens group is being detected. When the WLflag equals 1, the control circuit detects that the zoom lens group ispositioned at the wide terminus;

TL stands for the tele limit and is a flag for representing whether thetele terminus of the zooming lens group is being detected. When the TLflag=1, the control circuit detects that the zooming lens group ispositioned at the tele terminus;

MFL stands for the macro far limit and is a flag for representingwhether the far terminus of the focusing lens group is being detected bydriving the zooming lens group in the macro area. When the MFL flag=1,the control circuit detects that the zooming lens group is a tele macroby a signal that is being outputted from the zoom code plate 40 and thatthe lens group is positioned at the far terminus in the focus state;

MNL stands for the macro near limit and is a flag for representingwhether the near terminus of the focusing lens group is being detectedby driving the zooming lens group in the macro area. When the MNLflag=1, the control circuit detects that the zooming lens group is atele macro by a signal that is outputted from the zoom code plate 40 andthat the lens group is positioned at the near terminus in the focusstate;

SWREN is a release permission flag. When the SWREN flag=1, the releaseoperation is permitted, while when the SWREN flag=0, the releaseoperation is not permitted;

MF stands for manual focus and is a flag for representing whether amanual focus state takes place. When the MF flag=1, the manual focusstate takes place, while when MF=0, the manual focus state does not takeplace;

AF stands for auto focus and is a flag for representing whether anautofocus state takes place. When the AF flag=1, the autofocus statetakes place, while when AF=0, the auto focus state does not take place;

PZMACRO is a flag representing whether the zooming lens group ispositioned in the macro area by the power zoom mechanism. When thePZMACRO flag=1, the zooming lens group is positioned in the macro area;

AFGO is a flag representing whether the focusing lens group is beingdriven. When the AFGO flag=1, the focusing lens group is being driven byAF motor M1;

PZGO is a flag representing whether the zooming lens group is beingdriven. When the PZGO flag=1, the zooming lens group is being driven byPZ motor M2;

PZMGO is a flag representing whether the focusing lens group is beingdriven by the PZ motor M2 in the macro area. When the PZMGO flag=1, thefocusing lens group is being driven by PZ motor M2;

PZMODE is a flag representing whether the zooming lens group can bedriven by the power zoom mechanism. When the PZMODE flag=1, the zoominglens group can be driven;

MAGIMG is a flag representing whether to start the image magnificationconstant operation. When MAGIMG=1, the image magnification constantstart operation takes place;

ONIMG is a flag representing whether the image magnification constantcontrol operation takes place. When ONIMG=1, the image magnificationconstant operation takes place;

AFFARGO represents a process which drives the focusing lens group in thefar direction;

AFNEARGO represents a process which drives the focusing lens group inthe near direction;

AFDRVF is a flag representing a direction in which the focusing lens isdriven in the process. When AFDRVF=1, the focusing lens is driven in thefar direction, while when AFDRVF=0, it is driven in the near direction;

PZTELGO represents a process which drives the zooming lens group in thetele direction;

PZWIDEGO represents a process which drives it in the wide direction;

PZDRVF is a flag representing a direction in which the zooming lensgroup is driven in the process. When PZDRVF=1, the zooming lens group isdriven in the tele direction, while when PZDRVF=0, it is driven in thewide direction;

MCRFARGO represents a process which drives the zooming lens groupagainst the focusing lens group in the macro area;

MCRNEARGO represents a process which drives the zooming lens groupagainst the focusing lens group in the macro area;

MCRDRVF is a flag which represents a direction in which the zooming lensgroup is driven. When MCRDRVF=1, the zooming lens group is driven in thefar direction, while when MCRDRVF=0, it is driven in the near direction;

AFS is a flag representing whether an in-focus priority mode takesplace. When AFS=1, the in-focus priority mode takes place, while whenAFS=0, a release priority mode takes place;

AFCORR stands for AF correct. When a zoom operation is conducted in thein-focus priority state, the focal position may be moved depending on aphotographic lens (such as a variable focus lens). This flag is used tocompensate the focal position of the lens. When AFCORR=1, the focalposition being moved is compensated, while when AFCORR=0, it is notcompensated; and

ON/OFF of the macro switch represents whether or not the zooming lensgroup is positioned in the macro area.

The control operations of the camera control device structured asmentioned above are described using the flow charts illustrated in FIGS.14-42.

When the lock switch SWLOCK is turned ON, the control device, includingthe camera control circuit 4 and lens control circuit 5, executes aseries of instructions shown in FIG. 14. The control device isinitialized in step S1 by executing an initialization subroutine, shownin FIG. 34.

The initialization subroutine determines whether the AF mode switch(that is, the auto/manual selection mode switch SWAF A/M) has beenturned ON in step S1-1. When the AF mode switch has been turned ON, theautomatic focus operation is selected and processing advances to stepS1-2 to execute the AFFARGO subroutine, which is shown in FIG. 35. Whenthe switch is OFF, the manual operation is selected and processingadvances to step S1-26. The subroutine drives the focus lens, namely thefocusing lens group, to the far terminus in step S1-2.

The subroutine activates the AF motor drive section 45 so as to drivethe focusing lens group to the far terminus in step S-AFG1. The processsets the AFDRVF flag to 1, representing that the focusing lens group isbeing driven in the far direction in step S-AFG2. The process sets theAFGO flag to 1 to indicate that the focusing lens group is being drivenin step S-AFG3. The NL flag is set to 0 to indicate that the near limitof the focusing lens group has not been detected (step S-AFG4) and theFL flag is set to 0 to indicate that the far end has not been detected(step S-AFG5). After that, the subroutine returns to step S1-3 of theinitialize subroutine, shown in FIG. 34.

When the focusing lens is being driven to the far terminus, drivingpulses are outputted from the AF pulser 48 to the lens CPU 44. Thesubroutine determines whether the driving pulses are outputted from theAF pulser in S1-3. This determination is made by detecting whether thepulse interval is at least 100 msec. When a negative determination isobtained (i.e., a pulse interval of less than 100 msec), the subroutineenters a loop until the determined condition is affirmative (i.e., apulse interval of 100 msec or more). When the pulse interval exceeds 100msec, the focusing lens is driven and stopped at the far terminus. Atthis time, a friction type clutch, which is linked with the focusinglens group, slips. Thus, when the pulse interval exceeds 100 msec, thetest performed in step S1-3 is positive (i.e., the pulse interval is atleast 100 msec in duration) and processing advances to step S1-4 so asto execute an AFSTOP subroutine. The AFSTOP subroutine determineswhether the focusing lens group is being driven (AFGO=1) in step S-AS1,shown in FIG. 41. When the lens group is not being driven, AFGO=0 andprocessing returns to S1-5 of the initialize subroutine. When theprocess determines that the focusing lens group is being driven in stepS-AS1, AFGO is equal to 1. Thus, processing advances to step S-AS2 tostop AF motor M1 so as to stop driving the focusing lens group beforeadvancing to step S-AS3. This step sets the AFGO flag to 0. After that,processing returns to step S1-5 of the initialize subroutine.

In step S1-5, the FL flag is set to 1 to represent that the far terminusof the focusing lens group has been detected. At the present time, thefocusing lens group is not positioned at the near terminus, and thesubroutine advances to step S1-6 so as to set the NL flag to 0 torepresent that the near terminus of the focusing lens group has not beendetected, before proceeding to step S1-7.

If the subroutine determines that the AF switch, (i.e., the auto/manualselection switch SWAF A/M) has not been turned ON in step S1-1, it isunknown where the focusing lens group is positioned. Thus, processingadvances to steps S1-26 and S1-27, so as to set the FL flag and the NLflag to 0. Thereafter, processing advances to step S1-7.

In step S1-7, since the focusing lens block is positioned at the farterminus and the number of driving pulses from the far terminus for thefocusing lens group, P_(inf), is 0, the subroutine sets P_(inf) to 0.Thereafter, the WL flag (which represents whether the wide terminus ofthe zooming lens group is being detected) is set to 0, the TL flag (forrepresenting whether the tele terminus of the zooming lens group isbeing detected) is set to 0, the MFL flag (for representing whether thefar terminus of the focusing lens group is being detected by driving thezoom ring in the macro area) is set to 0, the MNL flag (for representingwhether the near terminus of the focusing lens group is being detectedby driving the zoom ring in the macro area) is set to 0, the SWREN flag(for representing whether the release operation is permitted) is set to0, the MF flag (for representing whether the manual focus state takesplace) is set to 0, and the AF flag (for representing whether theautofocus state takes place) is set to 0 (steps S1-8 to S1-14).Processing then advances to S1-15.

A determination is made as to whether the macro switch has been turnedON in step S1-15. When the determined condition is YES (ON), processingadvances to S1-16, so as to set the PZMACRO flag (for representingwhether the zooming lens group is positioned in the macro area by thepower zoom mechanism) to 1 before going to step S1-18. When thedetermined condition is NO (OFF), processing goes to step S1-17 so as toset the PZMACRO flag to 0 before advancing to step S1-18.

Next, the AFGO flag (for representing whether the focusing lens group isbeing driven) is set to 0, the PZGO flag (for representing whether thezooming lens group is being driven) is set to 0, the PZMGO flag (forrepresenting whether the zooming lens group is being driven by the PZmotor M2 in the macro area) is set to 0, the PZMODE flag (forrepresenting whether the zooming lens group can be driven by the powerzoom mechanism) is set to 0, the MAGIMG flag (for representing whetherto start the image magnification constant operation) is set to 0; theONIMG flag (for representing whether the image magnification constantcontrol operation takes place) is set to 0, a timer, such as a 5 msectimer, is started, and the timer is permitted to be interrupted in stepsS1-18 to S1-25, before processing returns to step S2 of the startprogram shown in FIG. 14.

In step S2, the program determines whether the AF mode switch, namelythe auto/manual selection switch SWAF A/M, has been turned ON. When theswitch has been turned ON, processing advances to S3. When the switchhas not been turned ON, processing advances to step S-M1, shown in FIG.21.

The next step determines whether the AF mode switch (switch SWAF A/M)has been turned ON and the AF operation (AF=1) takes place in step S-M1,shown in FIG. 21. When AF equals 1 (i.e., AF operation takes place),processing advances to step S-K1, shown in FIG. 30. When AF does notequal 1, the program sets the MF flag (for representing whether themanual focus state takes place) to 1 (in step S-M2), and advances tostep S-M3, so as to compute the amount of defocusing of the focusinglens group, dx.

Afterwards, a determination is made as to whether the contrast is LOW(step S-M4). When the contrast is LOW, processing advances to step S-M7so as to turn OFF the in-focus indication. When the contrast is not LOW,processing advances to step S-M5 to determine whether the image isfocused. If the image is not focused, processing advances to step S-M7,so as to turn OFF the in-focus indication. When the image is focused,processing advances to step S-M6 to turn ON the in-focus indication,before returning back to step S2, shown in FIG. 14, to determine whetherthe AF mode switch (switch SWAF A/M) has been turned ON (input). Whenthe manual mode takes place, processing enters into a loop between stepS-M1, shown in FIG. 21, and step S2, shown in FIG. 14, until the AF modeswitch is turned ON.

When AF=1 (i.e., AF operation state) in step S-M1 shown in FIG. 21,processing advances to step S-K1, shown in FIG. 30. This step prohibitsthe timer interrupt, before processing advances to step S-K2 to executean AFSTOP subroutine. The AFSTOP subroutine determines whether thefocusing lens group is being driven (AFGO=1) in step S-AS1, shown inFIG. 41. When the lens group is not being driven, processing advances tostep S-K3, which calls a ZOOMSTOP subroutine, shown in FIG. 42. WhenAFGO=1, AF motor M1 is stopped so as to stop driving the focusing lensgroup. Processing then advances to step S-K3, after the AFGO flag (forrepresenting whether the focusing lens group is being driven) is set to0 to call the ZOOMSTOP subroutine in FIG. 42.

The ZOOMSTOP subroutine determines whether the zooming lens group isbeing driven (PZGO=1) in step S-Z1, shown in FIG. 42. When PZGO is notequal to 1, processing advances to S-Z2, so as to determine whether theAF drive (autofocus drive) operation is being conducted by the powerzoom mechanism (PZ mechanism) in the macro area. When the AF driveoperation is not being conducted by the PZ mechanism (i.e., PZMGO=0),processing returns to step S-K4, shown in FIG. 30. When the zooming lensgroup is being driven (i.e., PZGO=1) in step S-Z1, or the AF driveoperation is being conducted (i.e., PZMGO=1) in S-Z2, processingadvances to step S-Z3, which stops PZ motor M2 so as to stop driving thezooming lens group. Thereafter, the PZGO flag (for representing whetherthe zooming lens group is being driven) and the PZMGO flag are each setto 0 (steps S-Z4 and S-Z5), before processing advances to step S-K4,shown in FIG. 30.

This step turns OFF the in-focus indication and then advances to stepS-K5, so as to determine whether the AF mode switch (switch SWAF A/M)has been turned ON. If the AF mode switch is OFF, processing advances tostep S-K6. If the AF mode switch is ON, processing advances to step S-K7to call an AFFARGO subroutine.

If step S-K6 is performed, the FL flag (for representing whether the farterminus of the focusing lens group is being detected) and the NL flag(for representing whether the near terminus of the focusing lens groupis being detected) are each set to 0. Processing then advances to stepS-K12.

When step S-K7 is performed, the AFFARGO subroutine, shown in FIG. 35 isperformed. In the same manner as described above, the process drives thefocusing lens group in the far direction, sets the AFDRVF and AFGO flagsto 1, sets the NL and FL flags to 0 and advances to step S-K8, shown inFIG. 30. When the focusing lens group is being driven in the fardirection, driving pulses are outputted from the AF pulser 48 to thelens CPU 44. The software program determines whether the driving pulsesare being outputted from the AF pulser 48 in step S-K8. Thisdetermination is made by detecting whether a pulse interval of at least100 msec occurs. When the pulse interval is less than 100 msec, thesoftware program enters a loop, until a pulse interval of at least 100msec is detected. When the pulse interval exceeds 100 msec, the focusinglens is driven and stopped at the far terminus. At this time, thefriction type clutch, which is linked with the focusing lens slips.Thus, when the pulse interval exceeds 100 msec, processing advances tostep S-K9 so as to execute the AFSTOP subroutine. This subroutinedetermines whether the focusing lens group is being driven (i.e.,AFGO=1), in step S-AS1, shown in FIG. 41. When the lens group is notbeing driven, AFGO=0 and processing advances to the ZOOMSTOP subroutinein step S-K3, shown in FIG. 30. When AFGO=1, AF motor M1 is stopped soas to stop the driving of the focusing lens group. Step S-AS3 is thenperformed to set the AFGO flag (for representing whether the focusinglens group is being driven) to 0 before advancing to step S-K10. The FLflag (for representing whether the far terminus of the focusing lensgroup is being detected) is then set to 1. Since the focusing lens groupis not positioned at the near terminus, processing advances to stepS-K11 to set the NL flag (for representing whether the near terminus ofthe focusing lens group is being detected) to 0 (steps S-K10 and S-K11).

Since the focusing lens group is positioned at the far terminus, thenumber of driving pulses from the far terminus for the focusing lensgroup, P_(inf), is set to 0 (step S-K12). Thereafter, the WL flag (forrepresenting whether the wide terminus of the zooming lens group isbeing detected), the TL flag (for representing whether the tele terminusof the zooming lens group is being detected), the MFL flag (forrepresenting whether the far terminus of the focusing lens group isbeing detected by driving the zoom ring in the macro area), the MNL flag(for representing whether the near terminus of the focusing lens groupis being detected by driving the zoom ring in the macro area), the ONIMGflag (for representing whether the image magnification constant controloperation takes place), the MAGIMG flag (for representing whether tostart the image magnification constant operation), the MF flag (forrepresenting whether the manual focus state takes place), the AF flag(for representing whether the autofocus state takes place), and theAFCORR flag (for representing whether to compensate the focus positionof the lens) are set to 0 in steps S-K13 to S-K18, the timer ispermitted to be interrupted in step S-K19, and then the software programreturns back to step S2, shown in FIG. 14.

When the program determines that the auto/manual selection switch SWAFA/M has been turned ON in step S2, processing advances to step S3. InS3, it is determined whether the MF flag (representing whether themanual focus state takes place) has been set to 1. When the focus statetakes place, an affirmative (YES) result is obtained and processingadvances to step S-K1. When the determined condition is negative,processing advances to step S4.

In step S4, it is determined whether the light metering SWS switch hasbeen turned ON. When the SWS switch is OFF, processing returns back tostep S2 so as to repeat the above operation until the SWS switch isturned ON. When the switch has been turned ON, processing advances tostep S5 to set the AF flag (representing whether the autofocus statetakes place) to 1. Next, the amount of defocusing of the focusing lensgroup dx is computed, in step S6, and it is determined whether thecontrast of the subject is LOW, using the amount of light from thesubject which enters into light reception element 10 (step S7). When thecontrast of the subject is LOW, processing returns back to step S2 torepeat the above operation until the contrast becomes HIGH. When thecontrast of subject is sufficient, processing advances to step S8. Thisstep determines whether the subject is focused. When the image is notfocused, processing advances to S9. When the image is focused,processing advances to step S21 to determine whether the imagemagnification constant mode switch SWPZC has been turned ON and theMAGIMG flag (representing whether to start the image magnificationconstant operation) has been set to 1. When the MAGIMG flag has been setto 1, processing turns OFF the in-focus indication (in step S25) andadvances to step S-B1, shown in FIG. 15. When the MAGIMG flag has notbeen set to 1, processing advances to step S22, turning ON the in-focusindication. Then, the SWREN flag (representing whether the releaseoperation is permitted) is set to 1 in step S23, and the softwareprogram advances to S24. This step determines whether the AF flag hasbeen set to 1; that is, whether the in-focus priority/release priorityselection switch SWAF S/C has been placed in the S position (in-focuspriority position) and the AFS flag (representing whether the in-focuspriority mode takes place) has been set to 1. When the determinedcondition is positive, the process enters a loop so as to lock thefocus. When the determined condition is negative, (that is, the switchhas been placed in the AFC position (release priority position)),processing returns back to step S2.

When it is determined that the subject is not focused in step S8,processing advances to step S9 to set the SWREN flag (representingwhether the release operation is permitted) to 0. Then, the in-focusindication is turned OFF. In step S11, the amount of driving of thefocusing lens group (dp), using the amount of defocusing dx obtained instep S6 is computed. In step S12, a determination is made as to whetherthe focusing lens group is being driven in the near direction. When thelens is being driven to the near direction, processing advances to stepS13. When the lens is in the far direction, processing advances to stepS18.

In step S13, it is determined whether the NL flag (representing whetherthe near terminus of the focusing lens group is being detected) has beenset to 1. That is, it is determined whether the focusing lens group ispositioned at the near limit (near terminus) in step S13. When thefocusing lens group is positioned at the near terminus (near limit) andthe NL flag has been set to 1, processing advances to step S-I1; shownin FIG. 20. When the focusing lens group is not positioned at the nearterminus (near limit), processing advances to step S14.

If step S18 is executed, the FL flag is checked to determine whether thefar terminus of the focusing lens group has been detected. When it hasbeen detected, the FL flag is set to 1, meaning that the focusing lensgroup is positioned at the far terminus (far limit). When the focusinglens group is positioned at the far terminus (far limit) and FL has beenset to 1, processing advances to step S-I1, shown in FIG. 20. When thefocusing lens group is not positioned at the far terminus (far limit),processing advances instead to step S19.

When the process advances to S-I1 shown in FIG. 20, a determination ismade whether the PZMODE flag (representing whether the zooming lensgroup can be driven by the power zoom mechanism) has been set to 1. Whenthe determined condition is negative, processing returns back to stepS2, shown in FIG. 14, until the determined condition becomes positive.When the determined condition is positive, processing advances to stepS-I2, so as to determine whether the macro switch has been turned ON andthe PZMACRO flag (representing whether the zooming lens group ispositioned in the macro area by the power zoom mechanism) has been setto 1. When the determined condition is negative, processing returns backto step S2, shown in FIG. 14, so as to enter a loop. When the determinedcondition is positive, processing advances to step S-I3, so as tocompute the amount of defocusing by driving the zooming lens group(zdpx) using the amount of defocusing dx described above. In step S-I4,it is determined whether the focusing direction of the zooming lensgroup is far or near. When it is determined that the lens is in the neardirection, processing advances to step S-I5. When it is determined thatthe lens is in the far direction, processing advances to step S-I12.

Step S-I5 determines whether the MNL flag (representing whether the nearterminus of the focusing lens group is being detected by driving thezoom ring in the macro area) has been set to 1. When the determinedcondition is positive, processing returns back to step S2, shown in FIG.14, so as to enter a loop. When the determined condition is negative,processing advances to step S-I6 to call a MCRNEARGO subroutine.

Step S-I12 determines whether the MFL flag (representing whether the farterminus of the focusing lens group is being detected by driving thezoom ring in the macro area) has been set to 1. When the determinedcondition is positive, processing returns back to step S2, shown in FIG.14, so as to enter a loop. When the determined condition is negative,processing advances to step S-I13 to execute a MCRFARGO subroutine.

The MCRNEARGO subroutine (called in step S-I6) drives the zooming lensgroup in the near direction, as shown in FIG. 40. The MCRFARGOsubroutine, called in step S-I13, drives the zooming lens group in thefar direction and is shown in FIG. 39.

The MCRNEARGO subroutine, shown in FIG. 40, activates PZ motor M2 instep S-MNG1, so as to drive the zooming lens group in the neardirection. Then, the MCRDRVF flag (representing whether the zooming lensgroup is being driven in the far direction in the macro area) is set to0 (i.e., near direction). The PZMGO flag (representing whether thezooming lens group is being driven by PZ motor M2 in the macro area) isset to 1 (i.e., drive state) and the TL flag (representing whether thetele terminus of the zooming lens group is being detected), the WL flag(representing whether the wide terminus of the zooming lens group isbeing detected), the MNL flag (representing whether the near terminus ofthe focusing lens group is being detected by driving the zoom ring inthe macro area) and the MFL flag (representing whether the far terminusof the focusing lens group is being detected by driving the zoom ring inthe macro area) are set to 0 in steps S-MNG3 to S-MNG7. After that,processing advances to step S-I7, shown in FIG. 20.

In the MCRFARGO subroutine, shown in FIG. 39, PZ motor M2 is activated(step S-MFG1) so as to drive the zooming lens group in the far terminus.Thereafter, the MCRDRVF flag (representing whether the zooming lensgroup is being driven in the far direction in the macro area) is set to1 (i.e., far direction) in step S-MFG2, and the PZMGO flag (representingwhether the zooming lens group is being driven by PZ motor M2 in themacro area) is set to 1 (i.e., drive state) in step S-MFG3. Then the TLflag (representing whether the tele terminus of the zooming lens groupis being detected), the WL flag (representing whether the wide terminusof the zooming lens group is being detected), the MNL flag (representingwhether the near terminus of the focusing lens group is being detectedby driving the zoom ring in the macro area) and the MFL flag(representing whether the far terminus of the focusing lens group isbeing detected by driving the zoom ring in the macro area) are set to 0in steps S-MFG4 to S-MFG7. Thereafter, processing advances to S-I7,shown in FIG. 20. When the zooming lens group is being driven, drivingpulses are outputted from PZ pulser 49 to the lens CPU 44.

In step S-I7, it is determined whether the zooming lens group has beendriven for the amount of focusing (zdpx) obtained in step S-I3. When thezooming lens group has been driven for an amount equal to zdpx,processing advances to step S-I14 so as to execute a ZOOMSTOPsubroutine, shown in FIG. 47, before returning back to step S2 in FIG.14. When the determined condition is negative, processing advances tostep S-I8.

In the step S-I8, it is determined whether the driving pulses are beingoutputted from the PZ pulser 49. This determination is made by detectingwhether the pulse interval is at least 100 msec. When the determinedcondition indicates a pulse interval of less than 100 msec, processingenters a loop until the determined condition indicates a pulse intervalof at least 100 msec. When the pulse interval equals or exceeds 100msec, the zooming lens group is driven and stopped at the far terminusor near terminus by executing the ZOOMSTOP subroutine called in eitherstep S-I14 or S-19. At this time, the friction type clutch, which linksPZ motor M2 and the zooming lens group, slips. Thus, when the pulseinterval equals or exceeds 100 msec, the determined condition ispositive (100 msec or more) and processing advances to step S-I9 so asto execute the ZOOMSTOP subroutine, shown in FIG. 42. Thereafter,processing advances to S-I10 to determine whether the driven directionwas near or far. When the determined condition is negative (i.e., neardirection), processing advances to step S-I11, so as to set the MNL flag(representing whether the near terminus of the focusing lens group isbeing detected by driving the zoom ring in the macro area) to 1, beforereturning back to step S2 in FIG. 14. When the determined condition ispositive (i.e., far direction), processing advances to step S-I12 to setthe MFL flag (representing whether the far terminus of the focusing lensgroup is being detected by driving the zoom ring in the macro area) to 1before returning back to step S2 in FIG. 14.

When processing advances from step S13 to S14 (FIG. 14), it drives thefocusing lens group in the near direction, as shown in FIG. 36. Whenprocessing advances from steps S18 to S19, it drives the focusing lensgroup in the far direction, as shown in FIG. 35.

The instructions shown in FIG. 35 drive the focusing lens group in thefar direction in step S-AFG1. The process sets the AFDRVF flag(representing whether the focusing lens group is being driven in the fardirection) to 1 (i.e., far direction) in step S-AFG2. Then, the AFGOflag (representing whether the focusing lens group is being driven) isset to 1 (i.e., drive state) in step S-AFG3, and the NL flag(representing whether the near terminus of the focusing lens group isbeing detected) and FL flag (representing whether the far terminus ofthe focusing lens group is being detected) are set to 0 in steps S-AFG4and S-AFG5, before advancing to step S15 in FIG. 14.

The instructions shown in FIG. 36 drive the focusing lens group in thenear direction in step S-ANG1. In step S-ANG2, since the drivingdirection of the focusing lens group is near rather than far, the AFDRVFflag (representing whether the focusing lens group is being driven inthe far direction) is set to 0 (i.e., near direction). The AFGO flag(representing whether the focusing lens group is being driven) is set to1 in step S-ANG3. The NL flag (representing whether the near terminus ofthe focusing lens group is being detected) and the FL flag (representingwhether the far terminus of the focusing lens group is being detected)are set to 0 in steps S-ANG4 and S-ANG5 before advancing to step S15 inFIG. 14.

In step S15, it is determined whether the focusing lens group has beendriven for the amount of defocusing dp obtained in step S6. When thefocusing lens group has been driven for an amount equal to dp,processing advances to step S20 to execute an AF drive stop subroutineto stop the focusing lens group, before returning back to step S2. Whenthe focusing lens group has not been driven by an amount equal to dp,processing advances to step S16 to determine whether the interval of thedriving pulses, which are outputted from the AF pulser 48, is at least100 msec. When the test indicates the pulse interval is less than 100msec, processing enters a loop so as to repeat steps S-15 and S-16. Whenthe pulse interval exceeds 100 msec, processing stops driving thefocusing lens group. At this time, the friction type clutch, which linksAF motor M1 and the focusing lens group, slips. Thus, when the pulseinterval exceeds 100 msec, processing advances to step S17 so as toexecute the AF terminus point subroutine. After that, processingadvances back to step S2.

AF Terminus Point Subroutine

The AF terminus point subroutine in step S17 is performed, as shown inFIG. 23. The AFSTOP subroutine, shown in FIG. 41, takes place in themanner as described above in step S-AFE1 to stop driving the focusinglens group, and then advances to step S-AFE2. The process computes thenumber of pulses being driven until the focusing lens group is stopped,dpx, using an output from the AF pulser 48 in step S-AFE2 beforeadvancing to step S-AFE3 to determine whether the driving direction ofthe focusing lens group is far. When the driving direction is far, thedetermined condition is YES and the process advances to step S-AFE12.When the driving direction is near, the determined condition is NO andprocessing advances to step S-AFE4.

In step S-AFE4, the process replaces the number of pulses for advancingthe focusing lens group P_(inf) with a value where the number of pulsesfor advancing the focusing lens group from the far terminus P_(inf) isadded to the number of pulses being driven until the focusing lens groupis stopped, dpx, obtained in step S-AFE2, before advancing to stepS-AFE5.

In step S-AFE5, the process subtracts the number of pulses between thefar terminus, P_(inf), and near terminus, Pnear, of the focusing lensfrom the number of pulses between the near terminus and the focal pointof the focusing lens group, P_(inf), obtained in step S-AFE4, to computean absolute value of the result as Plmt. After that, processing advancesto step S-AFE6.

In the terminus point detection process, since the number of pulsesbetween the far terminus and near terminus is known, it can be set asthe number of pulses for driving the focusing lens group to the nearterminus. However, it is necessary to consider that the focusing lensgroup may not be driven to the near terminus and stopped in the midwaydue to some cause.

On the other hand, since the number of pulses Pnear is a known valuefrom the lens being used, when the focusing lens group is positioned atthe near terminus, the result of the absolute value of the subtractionof P_(inf) -Pnear will be 0. Thus, when the focusing lens group ispositioned at the near terminus, the result of the subtraction should be0. However, if the result of the subtraction is in a predeterminedallowance, it is treated that the focusing lens group is positioned atthe terminus point. The number of pulses Pnear, which is a known valueof the lens, is stored in the lens ROM as fixed data.

Thus, the process determines whether the number of pulses at theterminus point is in a predetermined allowable value e or not. Namely,when .linevert split.P_(inf) -Pnear.linevert split. is less than theallowable value e, the determined condition is YES and processingadvances to step S-AFE10. Otherwise, the predetermined condition is NOand the process advances to step S-AFE7. The allowable value erepresents a range of pulses (such as 10 pulses) for which the focusinglens group can be driven without an error. In step S-AFE7, the processdrives the focusing lens group, shown in FIG. 36, on the near terminusside and then advances to step S-AFE8.

When the focusing lens group is being driven in the near direction,driving pulses are output from the AF pulser 48 to the lens CPU 44. Theprocess determines whether the driving pulses are being output from theAF pulser 48 in step S-AFE8. This determination is made by detectingwhether the pulse interval is at least 100 msec. When the determinedcondition is NO (less than 100 msec), the process enters a loop so as torepeat the test until the determined condition becomes YES (100 msec ormore), namely the terminus point is detected. When the pulse intervalexceeds 100 msec, the process drives the focusing lens group to the nearterminus and stops it. At this time, the friction type clutch, whichlinks AF motor M1 and the focusing lens group, slips. Thus, when thepulse interval exceeds 100 msec, the determined condition is YES (morethan 100 msec) and processing advances to step S-AFE9 to perform theAFSTOP subroutine shown in FIG. 41. After that, the process advances tostep S-AFE10 to set flag NL (representing whether the near terminus ofthe focusing lens group is being detected) to 1 in S-AFE10. Thereafter,the process equalizes P_(lmt) to Pnear in step S-AFE11 and advances toS2, shown in FIG. 14.

When the process determines that the driving direction is far in stepS-AFE3, the determined condition is YES (far direction) and the processadvances to step S-AFE12. At that time, the process replaces the numberof pulses for advancing the focusing lens group, P_(inf), with a valuewhere the number of pulses being driven until the focusing lens group isstopped, dpx, obtained in step S-AFE2 is subtracted from the number ofpulses for which the focusing lens group is advanced from the farterminus, P_(inf), and then advances to step S-AFE13.

In step S-AFE13, the process computes an absolute value .linevertsplit.P_(inf) -dpx.linevert split. for the number of pulses from thefocal point to the far terminus of the focusing lens group, P_(inf),obtained in step S-AFE12, and then advances to step S-AFE14. However,because the focusing lens group may not be driven to the far terminus,but rather stopped midway, it is necessary to detect that. On the otherhand, when the focusing lens group is positioned at the far terminus,the absolute value of P_(inf), namely the absolute value of P_(inf) -dpxin step S-AFE12 (result of the subtraction in steps-AFE12) will be 0.Thus, when the focusing lens group is positioned at the far terminus,the result of the subtraction should be 0. However, by considering thatsome error may occur, when the error is within an allowable value, it istreated as if the focusing lens group is positioned at the terminuspoint.

The process determines whether the number of pulses at the terminuspoint is in an allowable value e in step S-AFE14. In other words, when.linevert split.P_(inf) .linevert split. is less than the allowablevalue e, the determined condition is YES and the process advances tostep S-AFE18. Otherwise, the determined condition is NO and the processadvances to step S-AFE15 to drive the focusing lens group to the farterminus, shown in FIG. 35, in the manner described above.

When the focusing lens group is being driven to the far terminus,driving pulses are outputted from the AF pulser 48 to the lens CPU 44.The process determines whether the driving pulses are being output fromthe AF pulser 48 in step S-AFE16. This determination is made bydetecting whether the pulse interval is at least 100 msec. When thedetermined condition is NO (less than 100 msec), the process enters aloop so as to repeat the determination until the determined conditionbecomes YES (at least 100 msec), namely the terminus point is detected.When the pulse interval exceeds 100 msec, the process drives thefocusing lens group to the far terminus and stops it. At that time, thefriction type clutch, which links AF motor M1 and the focusing lensgroup, slips. Thus, when the pulse interval exceeds 100 msec, thedetermined condition is YES (more than 100 msec) and the processadvances to step S-AFE17 to perform the AFSTOP subroutine shown in FIG.41. The process then advances to step S-AFE18 to set flag FL(representing whether the far terminus of the focusing lens group isbeing detected) to 1 and P_(lmt) to 0 before advancing to step S2 inFIG. 14.

AF Drive Stop (FIG. 22)

The AF drive stop subroutine in step S20 is conducted as shown in FIG.22. The AFSTOP subroutine shown in FIG. 41 as described above takesplace in step S-AFS1 so as to stop driving, the focusing lens groupbefore advancing to step S-AFS2. The process computes the number ofpulses being driven until the focusing lens group is stopped, dpx, usingan output from the AF pulser 48 and then advances to step S-AFS3. Theprocess determines whether the driving direction is far in step S-AFS3.When the determined condition is YES (far direction), the processadvances to step S-AFS11. When the determined condition is NO (neardirection) the process advances to step S-AFS4.

The process replaces the number of pulses for advancing the focusinglens group, P_(inf), with a value where the number of pulses beingdriven until the focusing lens group is stopped, dpx (equivalent to dp)obtained in step S-AFS2 is added to the number of pulses for which thefocusing lens group is advanced from the far terminus, Pinf, beforeadvancing to step S-AFS5.

The process determines whether the number of pulses at the terminuspoint is larger (out of range) or smaller (in range) than Pnear in stepS-AFS5. When the determined condition is YES (in range), the processadvances to step S2 in FIG. 14. When the determined condition is NO (outof range), the process advances to step S-AFS6. The process drives thefocusing lens group in the near direction in step S-AFS6, shown in FIG.36.

When the focusing lens group is being driven in the near direction,driving pulses are output from the AF pulser 48 to the lens CPU 44. Theprocess determines whether the driving pulses are being output from theAF pulser 48 in step S-AFS7. This determination is made by detectingwhether the pulse interval is at least 100 msec. When the determinedcondition is NO (less than 100 msec), the process enters a loop so as torepeat the determination until the determined condition becomes YES (100msec or more), namely, the terminus point is detected. When the pulseinterval exceeds 100 msec, the process drives the focusing lens group tothe near terminus and stops it. At that time the friction type clutch,which links AF motor M1 and the focusing lens group, slips. Then, whenthe pulse interval exceeds 100 msec, the determined condition becomesYES (100 msec or more) and the process advances to step S-AFS8 toperform the AFSTOP subroutine shown in FIG. 41. Thereafter, the processadvances to step S-AFS9 and sets flag NL (representing whether the nearterminus of the focusing lens group is being detected) to 1. The processthen sets P_(inf) to be equal to Pnear in step S-AFS10 before advancingto step S2 in FIG. 14.

The process determines whether the driving direction is far in stepS-AFS3. When the determined condition is YES (far direction), theprocess advances to step S-AFS11. The process replaces the number ofpulses for which the focusing lens group is advanced, P_(inf), with avalue where the number of pulses being driven until the focusing lensgroup is stopped, dpx, obtained in step S-AFS2 is subtracted from thenumber of pulses for which the focusing lens group is advanced from thefar terminus, P_(inf), and then advances to step S-AFS12.

The process determines whether the number of pulses P_(inf) at theterminus point is larger (in range) or smaller (out of range) than 0 instep S-AFS12. When the determined condition is YES (in range), theprocess advances to step S2 in FIG. 14. When the determined condition isNO (out of range), the process advances to step S-AFS13. The processdrives the focusing lens group in the far direction in the mannerdescribed above and shown in FIG. 35 in step S-AFS13.

When the focusing lens group is being driven in the far direction,driving pulses are outputted from the AF pulser 48 to the lens CPU 44.The process determines whether the driving pulses are being output fromthe AF pulser 48 in step S-AFS14. This determination is made bydetecting whether the pulse interval is at least 100 msec. When thedetermined condition is NO (less than 100 msec), the process enters aloop so as to repeat the determination until the determined conditionbecomes YES (100 msec or more), namely the terminus point is detected.When the pulse interval exceeds 100 msec, the process drives thefocusing lens group to the far terminus and stops it. At that time, thefriction type clutch, which links AF motor M1 and the focusing lensgroup, slips. Thus, when the pulse interval exceeds 100 msec, thedetermined condition is YES (100 msec or more) and the process advancesto step S-AFS15 to execute the AFSTOP subroutine shown in FIG. 41 beforeadvancing to step S-AFS16 to set flag FL (representing whether the farterminus of the focusing lens group is being detected) to 1. Thereafter,P_(inf) is set to 0 in step S-AFS17, and processing advances to step S2in FIG. 14.

Image Magnification Constant Control

In step S21, shown in FIG. 14, the process determines whether flagMAGIMG (representing whether to start the image magnification constantoperation) has been set to 1. When the MAGIMG flag has been set to 1,the determined condition is YES and the process advances to step S25.The process turns OFF the in-focus indication in step S25. The processthen advances to step S-B1, shown in FIG. 15, to perform the imagemagnification constant control operation.

In step S-B1, shown in FIG. 15, the process sets flag ONIMG(representing whether the image magnification constant control operationtakes place) to 1 (control state). The process then advances to stepS-B2. The process computes the amount of advancing of the focusing lensgroup from the infinite terminus, x₀ in step S-B2 and then advances tostep S-B3. The process inputs the present focal length information ofthe zooming lens group, f₀, in step S-B3 and then advances to step S-B4.The process determines whether the amount of advancing, x₀, is smallerthan f₀ /150. In this determination, whether the amount of advancing,x₀, is smaller than f₀ /150 means whether the image magnification is toosmall to be controlled. When the image magnification is too small, achange of the image magnification, caused by a moving of the subject,cannot be precisely detected. Thus, in this case, when the determinedcondition is YES, the process advances to step S-B18 to turn OFF thein-focus indication. The process generates an out-of-control signal toinform the operator that the image magnification constant controloperation is disabled in step S-B19. The process sets flag SWREN(representing whether the release operation is permitted), flag ONIMG(representing whether the image magnification constant control operationtakes place) and flag MAGIMG (representing whether to start the imagemagnification constant operation) to 0 in steps S-B20 to S-B22, beforeadvancing to step S2 in FIG. 14.

When the process determines that the image magnification is not toosmall in step S-B4, the determined condition is NO and the processadvances to step S-B5. The process computes m₀ =x₀ /f₀ in step S-B5 andthen advances to step S-B6. The process computes the amount ofdefocusing, dx, in step S-B6 and advances to step S-B7 to determinewhether the contrast of the subject is LOW. When the determinedcondition is YES (LOW contrast), the process advances to step S-B23 toset flag SWREN (representing whether the release operation is permitted)to 0. The process turns OFF the in-focus indication in S-B24 and thenadvances to step S2 in FIG. 14 so as to enter a loop until the contrastbecomes HIGH. For improving the operability, this operation allows theimage magnification constant control operation to be continued when thesubject returns to a predetermined position on the screen, even if it islost from the screen or it has moved in a horizontal direction and thecontrast decreases.

When the determined condition is NO, the process advances to step S-B8to determine whether the subject is focused. When the determinedcondition is YES (focused), since the contrast is HIGH and the subjectdoes not move from the former position, the process advances to stepS-B16. The process then sets flag, SWREN (representing whether therelease operation is permitted) to 1 (release permission) in step S-B16and advances to step S-B17 so as to turn ON the in-focus indicationbefore returning back to step S-B1 so as to enter a loop. When thedetermined condition is NO (not focused) in step S-B8, since the lensshould be moved, the process advances to step S-B9. The process computesthe amount of driving of the focusing lens group, dp, using the amountof defocusing, dx, in step S-B9 and then advances to step S-B10.

The process computes a focal length of the focusing lens group of whichthe amount of defocusing dx occurs, using equation (7) in step S-B10 andthen advances to step S-B11. In this step, the focal length f ofequation (7) is assumed to be f1. Assuming that the focal length at thewide terminus of the focusing lens group is fW and that at the TLterminus it is ft, to perform the image magnification constant controloperation, it is necessary that fW<f1<ft. The process determines this instep S-B11. When f1 is not in the range, the determined condition is NOand the process advances to step S-B25. The process sets flag SWREN(representing whether the release operation is permitted) to 0 in stepS-B25 and then turns OFF the in-focus indication in step S-B26 beforeadvancing to step S-E1 in FIG. 18. The process starting at step S-E1waits until f1 is in the range of fW<f1<ft.

When f1 is in the range of fW<f1<ft in S-B11, the determined conditionis YES and the process advances to step S-B12. The process computes thecontrol image magnification, =f1/f₀, and then advances to step S-B13.The process inputs constants A, B, and C, for computing the amount ofdriving of the zooming lens group Pz, from the lens ROM 43 to the lensCPU 44 or main CPU 6 and then advances to step S-B14. The processcomputes the amount of driving Pz according to equation (11) using theconstants A, B, and C in step S-B14 and then advances to step S-B15 todetermine whether dp and Pz are 0. When both of them are not 0, thedetermined condition is NO and the process advances to step S-N1 in FIG.16. When both of them are 0, the determined condition is YES and theprocess advances to step S-B16 to set flag SWREN (representing whetherthe release operation is permitted) to 1 (release permission) and toturn ON the in-focus indication (in step S-B17) before returning back tostep S-B1 so as to enter a loop.

When the process determines that either dp or Pz is not 0 in S-B15, itadvances to step S-N1 in FIG. 16 to turn OFF the in-focus indication.The process then sets flag SWREN (representing whether the releaseoperation is permitted) to 0 in step S-N2 and advances to step S-N3 todetermine whether the amount of driving of the focusing lens group, dp,is 0. When the amount of driving is 0, the determined condition is YESand the process advances to step S-N9 to determine whether the amount ofdriving of the zooming lens group, Pz, is 0. When the amount of drivingof the zooming lens group Pz is 0, the determined condition is YES andthe process advances to step S-D1 in FIG. 17.

When the amount of driving dp is not 0 in step S-N3, the determinedcondition is NO and the process advances to step S-N4 to determinewhether the driving direction of the focusing lens group is far. Whenthe direction is near, the determined condition is NO and the processadvances to step S-N5. When the direction is far, the determinedcondition is YES and the process advances to step S-N7. The processdetermines whether flag NL (representing whether the near terminus ofthe focusing lens group is being detected) has been set to 1 in stepS-N5. When the terminus point has been detected and the NL flag has beenset to 1, the determined condition is YES and the process returns backto step S-B1 in FIG. 15 so as to enter a loop. When the determinedcondition is NO, the process advances to step S-N6. The processdetermines whether flag FL (representing whether the far terminus of thefocusing lens group is being detected), has been set to 1 in step S-N7.When the terminus point has been detected and the FL flag has been setto 1, the determined condition is YES and the process returns back tostep S-B1 in FIG. 15 so as to enter a loop. When the determinedcondition is NO, the process advances to step S-N8. The process in stepS-N6, shown in FIG. 35, is the AFFARGO subroutine which drives thefocusing lens group in the far direction. The subroutine in step S-N8,shown in FIG. 36, is the AFNEARGO subroutine which drives the focusinglens group in the near direction. After that, the process advances tostep S-N9 to determine whether the amount of driving, Pz, is 0. When itis not 0, the determined condition is NO and the process advances tostep S-N10 to determine whether the driving direction of the zoominglens group is towards the telephoto side. When the direction is towardsthe telephoto side, the determined condition is YES and the processadvances to step S-N11 to execute a PZTELEGO subroutine, shown in FIG.37, which drives the zooming lens group in the tele direction. When thedirection determination is wide in step S-N10, the determined conditionis NO and the process advances to step S-N12 to perform a PZWIDEGOsubroutine, shown in FIG. 38, which drives the zooming lens group in thewide direction.

The PZTELEGO subroutine, shown in FIG. 37, drives the zooming lens groupin the tele direction in step S-PTG1. The process then sets flag PZDRVT(representing whether the zooming lens group is being driven in the teledirection) to 1 (tele direction) and flag PZGO (representing whether thezooming lens group is being driven) to 1 (drive state) in steps S-PTG2and S-PTG3. In steps S-PTG4 to S-PTG7, the process sets flag TL(representing whether the tele terminus of the zooming lens group isbeing detected), flag WL (representing whether the wide terminus of thezooming lens group is being detected), flag MNL (representing whetherthe near terminus of the focusing lens group is being detected bydriving the zoom ring in the macro area) and flag MFL (representingwhether the far terminus of the focusing lens group is being detected bydriving the zoom ring in the macro area) to 0 before advancing to stepS-D1 in FIG. 17.

The PZWIDEGO subroutine, shown in FIG. 38, drives the zooming lens groupin the wide direction in step S-PWG1. The process sets flag PZDRVF(representing whether the zooming lens group is being driven in the teledirection) to 0 (wide direction) in step S-PWG2 and flag PZGO(representing whether the zooming lens group is being driven) to 1(drive state) in step S-PWG3. Thereafter, in steps S-PWG4 to S-PWG7, theprocess sets flag TL (representing whether the tele terminus of thezooming lens group is being detected), flag WL (representing whether thewide terminus of the zooming lens group is being detected), flag MNL(representing whether the near terminus of the focusing lens group isbeing detected by driving the zoom ring in the macro area) and flag MFL(representing whether the far terminus of the focusing lens group isbeing detected by driving the zoom ring in the macro area) beforeadvancing to step S-D1 in FIG. 17.

The process beginning at step S-D1 always stops at any position ratherthan detecting the terminus point, because the focusing lens group ispositioned in the zoom area. The process operates to only detect theterminus point of the focusing lens group. In the process starting atstep S-D1, the following cases are described:

(a) When both the focusing lens group and zooming lens group do notmove;

(b) When only the zooming lens group moves and the focusing lens groupdoes not move;

(c) When the zooming lens group stops and only the focusing lens groupmoves;

(d) When both the focusing lens group and the zooming lens group move(however, the focusing lens group stops earlier than the zooming lensgroup); and

(e) When both the focusing lens group and zooming lens group move(however, the zooming lens group stops earlier than the focusing lensgroup).

Each of the above cases is described below as follows:

(a) When Both the Focusing Lens Group and Zooming Lens Group Do Not Move

In step S-D1, shown in FIG. 17, the process determines whether flag AFGO(representing whether the focusing lens group is being driven) has beenset to 1 (drive state) When the determined condition is YES, the processadvances to step S-D2. When the determined condition is NO, the processadvances to step S-D13. The process determines whether flag PZGO(representing whether the zooming lens group is being driven) has beenset to 1 (drive state) in step S-D16. When the determined condition isNO, the process advances to step S-D16. The process sets flag SWREN(representing whether the release operation is permitted) to 1 (in-focusindication) in step S-D16, stops driving the focusing lens group, shownin FIG. 22, in step S-D17, and then advances to step S-D18.

The process then determines whether flag FL (representing whether thefar terminus of the focusing lens group is being detected) has been setto 0 (terminus point detection) in step S-D18. When the terminus pointhas been detected, the determined condition is YES and the processadvances to step S-B1 in FIG. 15 so as to enter a loop. When theterminus point has not been detected, the determined condition is NO andthe process advances to step S-D19. The process then determines whetherflag NL (representing whether the near terminus of the focusing lensgroup is being detected) has been set to 1 (terminus point detection) instep S-D19. When the determined condition is YES, the process advancesto step S-B1 in FIG. 15. When the terminus point has not been detected,the determined condition is NO and the process advances to step S-D20.

When the determined conditions in steps S-D18 and S-D19 are both NO,since the image magnification becomes constant, the process turns ON thein-focus indication in step S-D20. The process then sets flag SWREN(representing whether the releaseoperation is permitted) to 1 in stepS-D21 before returning back to step S-B1 in FIG. 15 so as to enter aloop. When either determined condition in step S-D18 or S-D19 is YES,the process returns back to step S-B1 in FIG. 15 so as to enter a loopuntil the image magnification becomes constant.

(b) When Only the Zooming Lens Group Moves and the Focusing Lens GroupDoes Not Move

The process determines whether flag AFGO (representing whether thefocusing lens group is being driven) has been set to 1 (drive state) instep S-D1. When the determined condition is YES, the process advances tostep S-D2. When the determined condition is NO, the process advances tostep S-D13. The process determines whether flag PZGO (representingwhether the zooming lens group is being driven) has been set to 1 (drivestate) in step S-D13. When the determined condition is YES, the processadvances to step S-D14. The process determines whether the zooming lensgroup has been driven for the number of driving pulses, Pz, in stepS-D14. When the determined condition is NO, the process returns back tostep S-D1 so as to enter a loop until the zooming lens group has beendriven for the number of driving pulses, Pz. When the zooming lens grouphas been driven for the number of driving pulses Pz, the determinedcondition in step S-D14 is YES (drive completion) and the processadvances to step S-D15. The process stops driving the zooming lens groupshown in FIG. 42 in step S-D15 and then advances to step S-D16. Afterthat, the process advances from steps S-D16 to S-D21 and then returnsback to step S-B1 in FIG. 15, so as to enter a loop.

(c) When the Zooming Lens Group Stops and Only the Focusing

Lens Group Moves

The process determines whether flag AFGO (representing whether thefocusing lens group is being driven) has been set to 1 (drive state) instep S-D1. When the determined condition is YES (drive state), theprocess advances to step S-D2. The process determines whether flag PZGO(representing whether the zooming lens group is being driven) has beenset to 1 (drive state) in step S-D2. When the determined condition is NO(non-drive state), the process advances to step S-D4. The processdetermines whether the focusing lens group has been driven for thenumber of pulses dp in step S-D4. When the determined condition is YES,the process advances to step S-D12 so as to perform the AFSTOPsubroutine shown in FIG. 41. The process stops driving the focusing lensgroup and then returns back to step S-D1 so as to enter a loop.

When the determined condition in step S-D4 is NO, the process advancesto step S-D5. The process determines whether the output interval of theAF pulses, which are output from the AF pulser 48, is at least 100 msecin step S-D5. When the determined condition is NO (less than 100 msec),the process returns back to step S-D1 so as to enter a loop until thepulse interval becomes 100 msec or more. When the determined conditionis YES (100 msec or more), the process advances to step S-D6 so as toperform the AFSTOP subroutine shown in FIG. 41. The subroutine stopsdriving the focusing lens group and then advances to step S-D7.

The process determines whether flag PZGO (representing whether thezooming lens group is being driven) has been set to 1 (drive state) instep S-D7. When the zooming lens group is not being driven, thedetermined condition is NO and the process advances to step S-D10. Theprocess advances to the terminus point process shown in FIG. 23 and thenreturns to step S-B1 in FIG. 15, so as to enter a loop.

(d) When Both the Focusing Lens Group and the Zooming Lens Group Move;However, the Focusing Lens Group Stops Earlier Than the Zooming LensGroup

The process determines whether flag AFGO (representing whether thefocusing lens group is being driven) has been set to 1 (drive state) instep S-D1. When the determined condition is YES (drive state), theprocess advances to step S-D2. The process then determines whether flagPZGO (representing whether the zooming lens group is being driven) hasbeen set to 1 (drive state) in step S-D2. When the determined conditionis YES (drive state), the process advances to step S-D3. The processdetermines whether the zooming lens group has been driven for therequired number of driving pulses Pz in step S-D3. When the determinedcondition is NO, the process advances to step S-D4 to determine whetherthe focusing lens group has been driven for the required number ofpulses dp. When the determined condition is YES, the process advances tostep S-D12 so as to perform the AFSTOP subroutine, shown in FIG. 41. Thesubroutine stops driving the focusing lens group, and then returns backto step S-D1, to advance to steps S-D13 to S-D19.

When the determined condition is NO in step S-D4, the process advancesto step S-D5 to determine whether the output interval of the AF pulses,which are outputted from the AF pulser 48, is at least 100 msec. Whenthe determined condition is NO (less than 100 msec), the process returnsback to step S-D1 so as to enter a loop until the pulse interval becomes100 msec or more. When the determined condition is YES (100 msec ormore), the process advances to step S-D6 so as to perform the AFSTOPsubroutine shown in FIG. 41, which stops driving the focusing lens groupand then advances to step S-D7.

The process then determines whether flag PZGO (representing whether thezooming lens group is being driven) has been set to 1 (drive state) instep S-D7. When the zooming lens group is being driven, the determinedcondition is YES and the process advances to step S-D8. The processdetermines whether the zooming lens group has been driven for the numberof driving pulses Pz based on the pulses which are outputted from the Pzpulser 49 in step S-D8. When the determined condition is NO, the processenters a loop until the zooming lens group has been driven for thenumber of driving pulses. When the determined condition is YES, theprocess advances to step S-D9 so as to stop driving the zooming lensgroup by executing a ZOOMSTOP subroutine, shown in FIG. 42 beforeadvancing to step S-D10 in FIG. 17 to perform the terminus point processsubroutine and then returning back to step S-B1 in FIG. 15, so as toenter a loop.

(e) When Both the Focusing Lens Group and Zooming Lens Group Move;However, the Zooming Lens Group Stops Earlier Than the Focusinq LensGroup

The process determines whether flag AFGO (representing whether thefocusing lens group is being driven) has been set to 1 (drive state) instep S-D1. When the determined condition is YES (drive state), theprocess advances to step S-D2. The process then determines whether flagPZGO (representing whether the zooming lens group is being driven) hasbeen set to 1 (drive state) in step S-D2. When the determined conditionis YES (drive state), the process advances to step S-D3. The processthen determines whether the zooming lens group has been driven for therequired number of driving pulses Pz in step S-D3. When the determinedcondition is YES, the process advances to step S-D11 to stop driving thezooming lens group before advancing to step S-D4.

The process determines whether the focusing lens group has been drivenfor the required number of pulses dp in step S-D4. When the determinedcondition is YES, the process advances to step S-D12 so as to performthe AFSTOP subroutine, shown in FIG. 41, to stop driving the focusinglens group before returning back to step S-D1. When the AFSTOPsubroutine is completed, flag AFGO (representing whether the focusinglens group is being driven) is set to 0. Thus, since the determinedcondition in step S-D1 is NO, the processes in steps S-D13 to S-D21 areperformed.

When the determined condition is NO in step S-D4, the process advancesto step S-D5 to determine whether the output interval of the AF pulses,which are outputted from the AF pulser 48, is at least 100 msec. Whenthe determined condition is NO (less than 100 msec), the process returnsback to step S-D1 so as to enter a loop until the output intervalbecomes 100 msec or more. When the determined condition is YES (100 msecor more), the process advances to step S-D6 to perform the AFSTOPsubroutine shown in FIG. 41, which stops driving the focusing lens groupbefore advancing to step S-D7.

The process determines whether flag PZGO (representing whether thezooming lens group is being driven) has been set to 1 (drive state) instep S-D7. When the zooming lens group is not being driven, thedetermined condition is NO and the process advances to step S-D10 toexecute the terminus point process subroutine shown in FIG. 23, beforereturning back to step S-B1 in FIG. 15 so as to enter a loop.

When the process advances to steps S-B25 and S-B26, based on thedetermined condition in step S-B11, processing advances to step S-E1 inFIG. 18. When the image magnification constant control is not in thezoom range, since it is preferable that the zooming lens group be movedto the terminus point rather than being placed midway for furtherprocessing, the process advances to step S-E1.

Whether the zooming lens group is positioned at the wide terminus ortele terminus is determined using f1. When f1 is smaller than ft, f1 issmaller than fw. Thus, by determining the sizes of f1 and ft only, thesize of f1 and fw can be determined at the same time, rather than havingto determine the sizes of f1 and ft and then f1 and fw.

Thus, the process determines whether f1 is equal to or larger than ft instep S-E1. When f1 is equal to or larger than ft, the zooming lens groupwill be positioned on the tele terminus side. Thus, the determinedcondition is YES and the process advances to step S-E2. When f1 issmaller than ft, the zooming lens group will be positioned on the wideterminus side. Thus, the determined condition is NO and the processadvances to step S-E13.

The process determines whether flag TL (representing whether the teleterminus of the zooming lens group is being detected) has been set to 1(terminus point detection) in step S-E2. When the terminus point hasbeen detected, the determined condition is YES and the process advancesto step S-E7. When the determined condition is NO, the process advancesto step S-E3. The process drives the zooming lens group in the teledirection, as shown in FIG. 37, in step S-E3 and then advances to stepS-E4. The process waits until the zooming lens group is positioned atthe terminus point in step S-E4. When the determined condition is NO(less than 100 msec), the process enters a loop until the determinedcondition becomes YES after the zooming lens group is detected at theterminus point. When the determined condition is YES (100 msec or more),the process advances to step S-E5 to perform a ZOOMSTOP subroutine shownin FIG. 42. The process stops driving the zooming lens group in stepS-E5 and then advances to step S-E6. The process sets flag TL(representing whether the tele terminus of the zooming lens group isbeing detected) to 1 in step S-E6 before advancing to step S-E7.

When the process advances from step S-E2 or S-E6 to step S-E7, itcomputes the amount of defocusing of the focusing lens group, dx, andthen advances to step S-E8 to determine whether the contrast of thesubject is LOW. When the contrast is LOW, the determined condition isYES and the process enters a loop until the proper contrast is present.When the proper contrast is present, the determined condition is NO andthe process advances to step S-E9. The process computes the amount ofadvancing of the focusing lens group, X₀, in step S-E9 and advances tostep S-E10. The process computes Xf=ft·m₀ in step S-E10 and thenadvances to step S-E11.

In step S-E11, the process determines whether or not the subject is inthe focal length of the image magnification m₀ obtained last time usingthe determination of whether dx+x₀ is larger than X_(f) obtained in stepS-E10. When the process determines that the subject is in the focallength, the determined condition is YES and the process advances to stepS-E12 to replace f₀ with ft and then advance to step S-B9 in FIG. 15 soas to start driving the focusing lens group. When the process determinesthat the subject is far from the focal length in step S-E11, thedetermined condition is NO and the process advances to step S-P1, shownin FIG. 19.

When the process determines that f1 is smaller than ft and that thefocusing lens group is positioned on the WL terminus side in step S-E1,the determined condition is NO, and the process advances to step S-E13to determine whether flag WL (representing whether the wide terminus ofthe zooming lens group is detected) has been set to 1 (terminus pointdetection). When the terminus point has been detected, the determinedcondition is YES and the process advances to step S-E18. When thedetermined condition is NO, the process advances to step S-E14, whichexecutes a subroutine to drive the zooming lens group in the widedirection, as shown in FIG. 38, and then advances to step S-E15. Theprocess waits until the zooming lens group detects the terminus point instep S-E15. When the determined condition is NO (less than 100 msec),the process enters a loop until the zooming lens group is positioned atthe terminus point and the determined condition becomes YES. When thedetermined condition is YES (100 msec or more), the process advances tostep S-E16 to perform the ZOOMSTOP subroutine shown in FIG. 42, whichstops driving the zooming lens group before advancing to step S-E17 toset flag WL (representing whether the wide terminus of the zooming lensgroup is being detected) to 1 before advancing to step S-E18.

When the process advances from step S-E13 or S-E17 to step S-E18, itcomputes the amount of defocusing of the focusing lens group, dx, instep S-E7 and then advances to step S-E19. The process determineswhether the contrast of the subject is LOW in step S-E19. When thecontrast is LOW, the determined condition is YES and the process entersa loop until the proper contrast is present. When the proper contrast ispresent, the determined condition is NO and the process advances to stepS-E20. The process computes the amount of advancing of the focusing lensgroup, x₀, in step S-E20 and then advances to step S-E21 to computex_(n) +fw·m₀ before advancing to step S-E22.

The process determines whether the subject is in the focal length of theimage magnification m₀ that was obtained last time using thedetermination of whether dx+x₀ is smaller than x_(n) in step S-E22. Whenthe subject is in the focal length in step S-E22, the determinedcondition is YES and the process advances to step S-E23 to replace f₀with fw. The process then advances to step S-B9 in FIG. 15 so as tostart driving the focusing lens group. When the process determines thatthe subject is nearer to the focal length, the determined condition isNO and the process advances to step S-P1, shown in FIG. 19.

The process computes the amount of driving of the focusing lens group,dp, using the amount of defocusing, dx, in step S-P1 before advancing tostep S-P2 to determine whether the driving direction of the focusinglens group is far. When the determined condition is NO (near direction),the process advances to step S-P3. When the determined condition is YES(far direction), the process advances to step S-P9. The processdetermines whether flag NL (representing whether the near terminus ofthe focusing lens group is being detected) has been set to 1 in stepS-P3. When the terminus point has been detected, the determinedcondition is YES and the process advances to step S-P8. When thedetermined condition is NO, the process advances to step S-P4. Theprocess determines whether flag FL (representing whether the farterminus of the focusing lens group is being detected) has been set to 1in step S-P9. When the terminus point has been detected, the determinedcondition is YES and the process advances to step S-P10. When thedetermined condition in step S-P3 is NO, the process advances to stepS-P4. The process drives the focusing lens group in the near direction,as shown in FIG. 36, in step S-P4. The process drives the focusing lensgroup in the far direction, as shown in FIG. 35, in step S-P10 and thenadvances to step S-P5.

The process determines whether the focusing lens group has been drivenfor the amount of driving dp. When the focusing lens group has beendriven for the amount of driving, the determined condition is YES andthe process advances to step S-P11 to perform the AF drive stopsubroutine, shown in FIG. 22, before advancing to step S-P8. When thedetermined condition is NO, the process advances to step S-P6 todetermine whether the interval of pulses, which are outputted from theAF pulser 48, is at least 100 msec. When the determined condition is NO(less than 100 msec), the process returns back to step S-P5 so as toenter a loop. When the determined condition is YES (100 msec or more),the process advances to step S-P7 so as to perform the AF terminus pointprocess subroutine shown in FIG. 23. The subroutine then advances tostep S-P8 to determine whether flag TL (representing whether the teleterminus of the zooming lens group is being detected) has been set to 1.When the terminus point has been detected, the determined condition isYES and the process advances to step S-E7, shown in FIG. 18. When thedetermined condition is NO, the process advances to step S-E18, shown inFIG. 18, so as to repeat the same operation.

Timer Interrupt Process

This process prohibits a timer interrupt in step S-T1, shown in FIG. 24,and then advances to step S-T2. The process turns ON the AF mode switch(switch SWAF A/M) and determines whether the AF mode takes place. Whenthe determined condition is YES (AF mode), the process advances to stepS-T3. When the determined condition is NO (manual mode), the processadvances to step S-T15 to determine whether the power zoom mode switchSWPZ has been turned ON. When the switch has been turned ON, thedetermined condition is YES and the process advances to step S-T16. Whenthe switch has been turned OFF, the determined condition is NO and theprocess advances to step S-T19. The process sets flag PZMODE(representing whether the zooming lens group can be driven by the powerzoom mechanism) to 1 (drive enable) in step S-T16 and sets flag PZMODEto 0 (drive disable) in step S-T19. After that, processing advances tostep S-T17 to determine whether flag AF (representing whether theautofocus state takes place) has been set to 1 (autofocus state) in stepS-T17. When the determined condition is YES, the process advances tostep S-K1 in FIG. 30. When the determined condition is NO, the processadvances to step S-T18, wherein a subroutine checks whether the powerzoom is driven (shown in FIG. 28) before advancing to step S-H1 in FIG.25.

The process determines whether the release switch SWR has been turned ONin step S-H1. When the switch has been turned ON, the determinedcondition is YES and the process advances to step S-H2. When the switchhas not been turned ON, the determined condition is NO and the processadvances to step S-H12 to execute a lens sheltering check subroutine,shown in FIG. 32, before advancing to step S-H13, in which a power zoomdrive check subroutine, shown in FIG. 28, takes place. Processing thenadvances to step S-H14 to permit a timer interrupt so as to complete thetimer interrupt process.

When the process determines that the release switch SWR has been turnedON in step S-H1, processing advances to step, S-H2, wherein adetermination is made as to whether flag MF (representing whether themanual focus state takes place) has been set to 1 (manual focusingstate). When the manual focus state takes place, the determinedcondition is YES and the process advances to step S-H5. When thedetermined condition is NO, the process advances to step S-H3. Theprocess determines whether the in-focus priority/release priorityselection switch SWF S/C has been placed in the in-focus priority (AFS)position or not in step S-H3. When the switch has been placed in theinfocus priority (AFS) position, the determined condition is YES and theprocess advances to step S-H4. When the switch has been placed in therelease priority (AFC) position, the determined condition is NO and theprocess advances to step S-H11. The process then determines whether flagONIMG (representing whether the image magnification constant controloperation takes place) has been set to 1 (image magnification constantstate) in step S-H11. When the image magnification constant state takesplace, the determined condition is YES and the process advances to stepS-H4. When the determined condition is NO, the process advances to stepS-H5. The process determines whether flag SWREN (representing whetherthe release operation is permitted) has been set to 1 (releasepermission) in step S-H4. When the determined condition is YES, theprocess advances to step S-H5. When the determined condition is NO, theprocess advances to steps S-H12 to S-H14 to complete the timer interruptprocess.

In step S-H5, the process determines whether flag AFGO (representingwhether the focusing lens group is being driven) has been set to 1(drive state). When the focusing lens group is being driven, thedetermined condition is YES and the process advances to step S-H6. Whenthe determined condition is NO, the process advances to step S-H10. TheAFSTOP subroutine, shown in FIG. 41, takes place in step S-H6 so as tostop driving the focusing lens group before advancing to step S-H7 tocompute the number of pulses being driven until the focusing lens groupis stopped, dpx, using an output from the AF pulser 48. Processing thenadvances to step S-H8 wherein a determination is made as to whether flagAFDRVF (representing whether the focusing lens group is being driven inthe far direction) has been set to 1 (far direction). When the directionis far, the determined condition is YES and the process advances to stepS-H15. When the determined condition is NO, the process advances to stepS-H9. The process replaces P_(inf) with P_(inf) -dpx (in step S-H15) orreplaces P_(inf) with P_(inf) +dpx (in step S-H9) before advancing tostep S-H10 to execute the ZOOMSTOP subroutine, shown in FIG. 42, so asto stop driving the zooming lens group and so that the process canadvance to step S-Q1, shown in FIG. 26, or step S-Q'1, shown in FIG. 27.

Release Process

(1) Release Process Q'

The release process, shown in FIG. 26, is continuously performed withoutdriving the focusing lens group and zooming lens group when the releaseswitch SWR has been turned ON in the continuous release mode (drive C).

When the process advances to step S-Q1, shown in FIG. 26, it performs arelease process to release the shutter of the camera. A lens shelteringcheck subroutine, shown in FIG. 32, takes place in step S-Q2 beforeprocessing advances to step S-Q3. When the operator controls the upswitch SWUP or down switch SWDOWN with the drive switch SWDRIVE, theprocess enters the drive C mode, namely continuous release mode (wherethe release process is continuously performed) or drive S mode, namelysingle release mode (where the release process is performed once) andthen advances to step S-Q4 to determine whether the drive mode is driveS. When the drive mode is drive C mode, the determined condition is NOand the process advances to step S-Q5. When the drive mode is drive S.the determined condition is YES and the process advances to step S-Q6.The process determines whether the release switch SWR has been turned ONin step S-Q5. When the switch has been turned ON, the determinedcondition is YES and the process returns back to step S-Q1, so as tocontinuously perform the release process in a loop until the switch isturned OFF. When the switch has been turned OFF, the determinedcondition is NO and the process advances to step S-Q7. The process alsodetermines whether the release switch SWR has been turned ON or OFF instep S-Q6. When the process has been turned ON, the determined conditionis YES and processing returns back to step S-Q2 so as to enter a loopuntil the switch is turned OFF. When the switch has been turned OFF, thedetermined condition is NO and the process advances to step S-Q7 todetermine whether the light metering switch SWS has been turned ON. Whenthe switch has not been turned ON, the determined condition is NO andthe process advances to step S-L1, in FIG. 31. When the switch has beenturned ON, the determined condition is YES and the process advances tostep S-Q8.

The process prohibits the timer interrupt in step S-L1, shown in FIG.31, and then advances to S-L2 to execute the AFSTOP subroutine, shown inFIG. 41, to stop the focusing lens group before advancing to step S-L3to determine whether flag ONIMG (representing whether the imagemagnification constant control operation takes place) has been set to 1(image magnification constant control state). When the control operationdoes not take place, the determined condition is NO and the processadvances to step S-L7. When the control operation takes place, thedetermined condition is YES and the process advances to step S-L4. TheZOOMSTOP subroutine, shown in FIG. 42, stops the zooming lens group andthen advances to step S-L5 to set flag MAGIMG (representing whether tostart the image magnification constant operation) to 0. In step S-L6,flag ONIMG (representing whether the image magnification constantcontrol operation takes place) is set to 0. The process then sets flagSWREN (representing whether the release operation is permitted) to 0(non-permission) and flag AFCORR (representing whether to compensate thefocus position of the lens) to 0 in steps S-L7 and S-L8. The AF drivestop subroutine, shown in FIG. 22, takes place in step S-L9 and then theprocess advances to step S-10 to permit the timer interrupt beforereturning back to step S2 in FIG. 14.

When the process advances from step S-Q7 to S-Q8 in FIG. 26, itdetermines whether flag AF (representing whether the autofocus statetakes place) has been set to 1 (autofocus state). When the autofocusstate takes place, the determined condition is YES and the processadvances to step S-Q9 to determine whether flag ONIMG (representingwhether the image magnification constant control operation takes place)has been set to 1 (image magnification constant control state). When thecontrol state does not take place, the determined condition is NO andthe process advances to step S-Q11. Alternatively, when the determinedcondition in step S-Q8 is NO, the process advances to step S-Q11. Whenthe control state in step S-Q9 takes place, the determined condition isYES and the process advances to step S-Q10. The process permits thetimer interrupt in step S-Q10 and then returns back to step S-B1 in FIG.15. The process also permits the timer interrupt in step S-Q11 beforereturning back to step S2 in FIG. 14.

(2) Release Process Q'

The release process Q' shown in FIG. 27 performs the release permissionwhich is preceded by a repeated AF operation and image magnificationconstant control operation, regardless of whether the release switch SWRhas been turned ON/OFF when the drive mode is in the continuous releasemode (drive C) and the in-focus priority mode takes place. In otherwords, the processes in steps S-Q'5 and S-Q'6 perform the releaseoperation after determining whether the AF mode and in-focus prioritymode takes place.

The release process in step S-Q'1 releases the shutter of the camera andthen advances to step S-Q'2 to execute the lens sheltering checksubroutine that is shown in FIG. 32. Processing then advances to stepS-Q'3. When the operator controls the up switch SWUP or down switchSWDOWN with the drive switch SWDRIVE operated, the process enters thedrive C mode, namely the continuous release mode (where the releaseprocess is continuously performed) or the drive S mode, namely thesingle release mode (where the release process is performed once) andthen advances to step S-Q'4 to determine whether the drive mode is thedrive S mode. When the drive mode is drive C mode, the determinedcondition is NO and the process advances to step S-Q'5. When the drivemode is the drive S mode, the determined condition is YES and theprocess advances to step S-Q'7.

The process determines whether the release switch SWR has been turned ONin step S-Q'7. When the switch has been turned ON, the determinedcondition is YES and the process returns back to step S-Q'2 so as toenter a loop until the switch is turned OFF. When the switch has beenturned OFF, the determined condition is NO and the process advances tostep S-Q'9.

The process determines whether the AF mode switch (switch SWAF A/M) hasbeen turned ON in step S-Q'5. When the switch has been turned ON, thedetermined condition is YES (AF mode) and the process advances to stepS-Q'6. When the switch has been turned OFF, the determined condition isNO (manual) and the process advances to step S-Q'8. In step S-Q'6, theprocess determines whether the in-focus priority/release priorityselection switch SWF S/C has been placed in the in-focus priorityposition (AFS). When the switch has been placed in the in-focus priorityposition, the determined condition is YES and the process advances tostep S-Q'9. When the determined condition is NO, the process advances tostep S-Q'8.

In step S-Q'8, the process determines whether the release switch SWR hasbeen turned ON. When the switch has been turned ON, the determinedcondition is YES and the process returns back to step S-Q'1, so as tocontinuously perform the release process in a loop until the switch isturned OFF. When the switch has been turned OFF, the determinedcondition is NO and the process advances to step S-Q'9.

The process executed in step S-Q'9 sets flag SWREN (representing whetherthe release operation is permitted) to 0 and then advances to stepS-Q'10 to determine whether flag AF (representing whether the autofocusstate takes place) has been set to 1 (autofocus). When the autofocusstate takes place, the determined condition is YES and the processadvances to step S-Q'11. However, when the determined condition is NO,the process advances to step S-Q'13. When processing advances from stepS-Q'10 to S-Q'11, a determination is made as to whether flag ONIMG(representing whether the image magnification constant control operationtakes place) has been set to 1 (image magnification constant controlstate). When the control state does take place, the determined conditionis YES and the process advances to step S-Q'12. When the control statedoes not take place, the determined condition is NO and the processadvances to step S-Q'13. The process permits the timer interrupt in stepS-Q'12 and then returns back to step S-B1 in FIG. 15. The processpermits the timer interrupt in S-Q'13 and then returns back to step S2shown in FIG. 14.

When the process determines that the manual mode takes place in stepS-T2 in FIG. 24, the processes in steps S-T15 to S-T18, the processbeginning at step S-K1 in FIG. 30, the process beginning at step S-H1shown in FIG. 25, the process beginning at step S-Q1 in FIG. 26 or theprocess beginning at step S-Q'1 in FIG. 27, and the process beginning atstep S-L1 in FIG. 31 take place. When the process determines that the AFmode switch (switch SWAF A/M) has been turned OFF in step S-T2, thedetermined condition is NO (AF) and the process advances to step S-T3.

The process determines whether the in-focus priority mode takes place instep S-T3. When the mode is the in-focus mode, the process advances tostep S-T20 to set flag AFS (representing whether the in-focus prioritymode takes place) to 1 (in-focus priority) before advancing to stepS-T7. When the process determines that the mode is not the in-focuspriority mode in S-T3, the determined condition is NO and the processadvances to step S-T4 to set flag AFS (representing whether the in-focuspriority mode takes place) to 0. Since the release operation can beperformed at any time, the process sets flag SWREN (representing whetherthe release operation is permitted) to 0 in step S-T5 so that the AFprocess can be performed even if the focal point is moved after thesubject is focused. In other words, even if the subject is focused inthe in-focus priority mode, the in-focus state cannot always bedetected. When the present mode is changed to another mode, it isnecessary to perform the AF process once again.

When the zooming lens group is driven and zoomed after the subject isfocused, the focal point may be moved depending on the type of thephotographic lens used, such as a variable focal lens. When the variablefocal lens is zoomed by driving the zooming lens group, the focal pointis moved. Thus, the focal point must be compensated. In the in-focuspriority mode, it is necessary to set flag AFCORR to 1 and perform theAF operation once again. However, since the present mode is not thein-focus priority mode, the process sets flag AFCORR (representingwhether to compensate the focus position of the lens) to 0 in step S-T6and then advances to step S-T7.

The process determines whether the light metering switch SWS has beenturned ON in step S-T7. When the switch has been turned ON, thedetermined condition is YES and the process advances to step S-T9,without checking the AF bit. When the switch is OFF, the determinedcondition is NO and the process advances to step S-T8 so as to check theAF bit. The process determines whether flag AF (representing whether theautofocus state takes place) has been set to 1 (autofocus state) in stepS-T8. When the autofocus state takes place, the determined condition isYES and the process advances to step S-L2 in FIG. 31. When thedetermined condition is NO, the process advances to step S-T9.

The process determines whether the power zoom switch SWPZ has beenturned ON in step S-T9. When the switch has been turned OFF, thedetermined condition is NO and the process advances to step S-T21. Whenthe switch has been turned ON, the determined condition is YES and theprocess advances to step S-T10 to set flag PZMODE (representing whetherthe zooming lens group can be driven by the power zoom mechanism) to 1(drive state) before advancing to step S-T11. Alternatively, the processsets flag PZMODE to 0 in step S-T21 and then advances to step S-T22 toexecute the ZOOMSTOP subroutine, shown in FIG. 42. Processing thenadvances to step S-T23.

Regardless of whether the zoom switch SWPZ has been turned ON or OFF,the zooming lens group may have been manually moved to the macro area.In addition, although the zooming lens group is driven and controlledregardless of whether it is positioned in the zoom area or macro area,the drive control method depends on the area where the zooming lens ispositioned. Thus, the process determines whether the macro switch hasbeen turned ON in steps S-T11 and S-T23.

When the process determined that the macro switch SWPZC has been turnedON in step S-T23, the determined condition is YES and the processadvances to step S-T24 to set flag PZMACRO (representing whether thezooming lens group is positioned in the macro area by the power zoommechanism) to 1 (macro area). When the switch has not been turned ON,the determined condition is NO and the process advances to step S-T25 toset flag PZMACRO to 0 (zoom area) in step S-T25, so as to perform theprocess beginning at step S-H1.

When the process determines that the macro switch has been turned ON instep S-T11, the determined condition is YES and the process advances tostep S-T26. When the switch has not been turned ON, the determinedcondition is NO and the process advances to step S-T12. The processdetermines whether flag PZMACRO (representing whether the zooming lensgroup is positioned in the macro area by the power zoom mechanism) hasbeen set to 1 (macro area) in step S-T26. When the zooming lens grouphas been positioned in the macro area, the determined condition is YESand the process advances to step S-T30. When the zooming lens group hasnot been positioned in the macro area, the determined condition is NOand the process advances to steps S-T27 to S-T29 to set flag MNL(representing whether the near terminus of the focusing lens group isbeing detected by driving the zoom ring in the macro area) and flag MFL(representing whether the far terminus of the focusing lens group isbeing detected by driving the zoom ring in the macro area) to 0 and flagPZMACRO (representing whether the zooming lens group is positioned inthe macro area by the power zoom mechanism) to 1 (macro area) beforeadvancing to step S-T30. Since the image magnification constant controloperation cannot be performed in the macro area, the process sets flagMAGIMG (representing whether to start the image magnification constantoperation) to 0 in step S-T30 and then advances to step S-T31 todetermine whether flag ONIMG (representing whether the imagemagnification constant control operation takes place) has been set to 1(control state). When the control operation is being performed, thedetermined condition is YES and the process advances to step S-L1 inFIG. 31 so as to stop the image magnification constant controloperation. When the control operation is not being performed, thedetermined condition is NO and the process advances to step S-T32 toexecute the power zoom drive check subroutine, shown in FIG. 28, beforeadvancing to step S-H1 in FIG. 25 so as to perform the release process.

When the process advances from step S-T11 to step S-T12, the processdetermines whether flag PZMACRO (representing whether the zooming lensgroup is positioned in the macro area by the power zoom mechanism) hasbeen set to 1 (macro area). When the zooming lens group has beenpositioned in the macro area, the determined condition is YES and theprocess advances to step S-T33. When the zooming lens group has not beenpositioned in the macro area, the determined condition is NO and theprocess advances to step S-T13. The process sets flag PZMACRO to 0 (zoomarea, rather than macro area) in step S-T33 and then advances to stepS-K1 in FIG. 30.

When the process advances from step S-T12 to step S-T13, the processdetermines whether the image magnification constant mode switch SWPZChas been turned ON. When the switch has not been turned ON, thedetermined condition is NO and the process advances to steps S-T30 andS-T31, described above. After that, the process advances to step S-L1 inFIG. 31, so as to stop the image magnification constant controloperation. When the switch has been turned ON, the determined conditionis YES and the process advances to step S-T14 to set flag PZMACRO(representing whether the zooming lens group is positioned in the macroarea by the power zoom mechanism) to 1 in step S-T14 and advances tostep S-H1 in FIG. 25 so as to perform the release process.

Power Zoom Drive Check

This process determines whether the power zoom mode switch SWPZ has beenturned ON and flag PZMODE (representing whether the zooming lens groupcan be driven by the power zoom mechanism) has been set to 1 (driveenable) in step S-PD1 in FIG. 28. When the power zoom can be driven, thedetermined condition is YES and the process advances to step S-PD2. Whenthe power zoom cannot be driven, the determined condition is NO and theprocess advances to step S-PD7. The process determines whether thezooming lens group is being driven by the power zoom mechanism, bychecking to see if flag PZGO (representing whether the zooming lensgroup is being driven) has been set to 1 (drive state) in step S-PD7.When the zooming lens group is not being driven, the process advances toa step following the power zoom drive check process. When the zoominglens group is being driven, the determined condition is YES and theprocess advances to step S-PD8 to execute the ZOOMSTOP subroutine shownin FIG. 42 to stop the zooming lens group, before advancing to stepS-PD17.

When the process determines that flag PZMODE (representing whether thezooming lens group can be driven by the power zoom mechanism) has beenset to 1 (drive enable) in step S-PD1, the determined condition is YESand the process advances to step S-PD2 to determine whether flag ONIMG(representing whether the image magnification constant control operationtakes place) has been set to 1 (control state). When the controloperation is being performed, the determined condition is YES and theprocess advances to a step following the power zoom drive check process.When the determined condition is NO, the process advances to step S-PD3.The process determines whether flag PZMGO (representing whether thezooming lens group is being driven by PZ motor M2 in the macro area) hasbeen set to 1 (drive state) in step S-PD3. When the zooming lens groupis being driven, the determined condition is YES and the processadvances to a step following the power zoom drive check process. Whenthe determined condition is NO, the process advances to step S-PD4.

The process determines whether the zooming switch SWPZW (for driving thezooming lens group in the wide direction) has been turned ON in stepS-PD4. When the switch has been turned ON, the determined condition isYES and the process advances to step S-PD5. When the determinedcondition is NO, the process advances to step S-PD9 to determine whetherthe zoom switch SWPZT (for driving the zooming lens group in the teledirection) has been turned ON. When the switch has been turned ON, thedetermined condition is YES and the process advances to step S-PD10 whenthe determined condition is NO, the process advances to step S-PD7. Theprocess determines whether flag PZGO (representing whether the zoominglens group is being driven) has been set to 1 (drive state) in stepS-PD5. When the zooming lens group is not being driven, the determinedcondition is NO and the process advances to step S-PD22. When thezooming lens group is being driven, the determined condition is YES andthe process advances to step S-PD6. The process determines whether flagPZGO has been set to 1 (drive state) in step S-PD10. When the lens groupis not being driven, the determined condition is NO and the processadvances to step S-PD22. When the lens group is being driven, thedetermined condition is YES and the process advances to step S-PD11.

When the zooming lens group is being moved to the tele side, while thezoom switch SWPZW for driving the zooming lens group in the widedirection has been turned ON and the zooming lens group is being driven,a contradiction occurs. Thus, the process determines whether flag PZDRVT(representing whether the zooming lens group is being driven on the teleside) has been set to 1 (being driven to the tele side) in step S-PD6.When the zooming lens is being driven on the tele side, a contradictionoccurs. Thus, the determined condition is YES and the process advancesto step S-PD8 so as to perform the ZOOMSTOP subroutine, which stops thezooming lens group.

In addition, when the zooming lens group is being moved on the wide sidewhile the zoom switch SWPZT for driving the zooming lens group in thetele direction has been turned ON and the zooming lens group is beingdriven, a contradiction occurs. Thus, the process determines whetherflag PZDRVT (representing whether the zooming lens group is being drivenon the tele side) has been set to 1 (being driven on tele side) in stepS-PD11. When the zooming lens group is being driven on the wide side, acontradiction occurs. In this case, the determined condition is NO andthe process advances to step S-PD8 so as to execute the ZOOMSTOPsubroutine, which stops the zooming lens group.

On the other hand, when the process determines that the zooming lensgroup is not being driven on the tele side in step S-PD6, nocontradiction occurs. In this case, the determined condition is NO andthe process advances to step S-PD12. Also, when the process determinesthat the zooming lens group is not being driven on the wide side in stepS-PD11, namely the lens is being driven on the tele side, nocontradiction occurs. In this case, the determined condition is YES andthe process advances to step S-PD12. In step S-PD12, the processdetermines whether the interval of the pulses being outputted from thePZ pulser 49 is at least 100 msec. When the pulse interval is less than100 msec, the determined condition is NO and the process advances to astep following the power zoom drive check process. When the outputterminal is 100 msec or more, the determined condition is YES and theprocess advances to the ZOOMSTOP subroutine, shown in FIG. 42, whichstops the zooming lens group. The process then advances to step S-PD14to determine whether flag PZDRVT (representing whether the zooming lensgroup is being driven on the tele side) has been set to 1 (being drivenon tele side). When the zooming lens group is being driven on the teleside, the determined condition is YES and the process advances to stepS-PD16. When the zooming lens group is being driven on the wide side,rather than the tele side, the determined condition is NO and theprocess advances to step S-PD15, wherein flag WL (representing whetherthe wide terminus of the zooming lens group is being detected) is set to1 and then advances to step S-PD17. The process sets flag TL(representing whether the tele terminus of the zooming lens group isbeing detected) to 1 in step S-PD16 and then also advances to stepS-PD17.

When the process advances from steps S-PD5 and S-PD10 to step S-PD22, itset flag AFCORR (representing whether to compensate the focus positionof the lens) to 0. The process then determines in which direction, teleor wide, the zooming lens group is being driven to by which zoom switch,SWPZT or SWPZW. When the zoom switch SWPZT has been turned ON, theprocess advances to step S-PD26. When the zoom switch SWPZW has beenturned ON, the process advances to step S-PD24.

In step S-PD24, the process determines whether flag WL (representingwhether the wide terminus of the zooming lens group is being detected)has been set to 1. In step S-PD26, the process determines whether flagTL (representing whether the tele terminus of the zooming lens group isbeing detected) has been set to 1. When the determined condition in stepS-PD24 or step S-PD26 is YES, the process advances to a step followingthe power zoom drive check process. When the determined condition instep S-PD24 or step S-PD26 is NO, the process advances to steps S-PD25and S-PD27, respectively.

The PZWIDEGO subroutine, shown in FIG. 38, drives the zooming lens groupin the wide direction. The PZTELEGO subroutine, shown in FIG. 37, drivesthe zooming lens group in the tele direction. When each subroutine hascompleted its execution, processing advances to step S-PD28.

The process determines whether flag AF (representing whether theautofocus state takes place) has been set to 1 (autofocus state) in stepS-PD28. When the autofocus state takes place, the determined conditionis YES and control advances to step S-PD29 to determine whether thein-focus priority/release priority selection switch SWF S/C has beenplaced in the in-focus priority (AFS) position. When the switch has beenplaced in the in-focus priority position, the determined condition isYES and the process advances to step S-PD30 to determine whether flagSWREN (representing whether the release operation is permitted) has beenset to 1 (release permission). When the release operation has beenpermitted, the process advances to step S-PD31 to determine whether thephotographic lens 3 is a variable focal lens, based on the informationstored in the lens ROM 43. When the photographic lens is a variablefocal, the determined condition is YES and the process advances to stepS-PD32. When the determined condition in steps S-PD28 to S-PD31 is NO,the process advances to a step following the power zoom drive checkprocess.

When the process advances from step S-PD31 to step S-PD32, it stores thefocal length PZSTARTF at which the zooming lens group is driven in stepS-PD32 and advances to step S-PD33 to set flag SWREN (representingwhether the release operation is permitted) to 0 (non-releasepermission) and advances to step S-PD35 to set flag AFCORR (representingwhether to compensate the focus position of the lens) to 1 after turningOFF the in-focus indication in step S-PD34. Processing then advances toa step following the power zoom drive check process.

When the process advances from step S-PD8, step S-PD15 or step S-PD16 tostep S-PD17, a determination is made as to whether flag AF (representingwhether the autofocus state takes place) has been set to 1 (autofocusstate). When the autofocus state takes place, the determined conditionis YES and the process advances to step S-PD18 to determine whether thein-focus priority/release priority selection switch SWF S/C has beenplaced in the in-focus priority (AFS) position. When the in-focuspriority mode takes place, the determined condition is YES and theprocess-advances to step S-PD19 to determine whether flag AFCORR(representing whether to compensate the focus position of the lens) hasbeen set to 1. When the determined condition is YES, the processadvances to step S-PD20. The process stores the focus length PZENDF, atwhich the zooming lens group is stopped, in step S-PD20 and advances tostep S-R1 in FIG. 29, or alternatively, to step S2 in FIG. 14. When thedetermined condition in steps S-P17 to S-P19 is NO, the process advancesto a step following the power zoom drive check process.

The process reads a compensation value PSTRT corresponding to the focallength PZSTART at which the zooming lens group is driven from the lensROM 43 in step S-R1. In step S-R2, the process reads a compensationvalue PEND, corresponding to the focal length PZENDF at which thezooming lens group is stopped, from the lens ROM 43 and advances to stepS-R3. The compensation value is the amount of deviation of the focallength caused by the zooming lens group being driven when a variablefocal lens is used as the photographic lens. The amount of deviation(compensation value) is listed in Table 2.

                  TABLE 2                                                         ______________________________________                                                     Compensation Pulse                                               Focal Length (Compensation Value n)                                           ______________________________________                                         70          n.sub.1                                                           79          n.sub.2                                                           89          n.sub.3                                                          101          n.sub.4                                                          114          n.sub.5                                                          129          n.sub.6                                                          146          n.sub.7                                                          165          n.sub.8                                                          165          n.sub.9                                                          186          .sub. n.sub.10                                                   210          .sub. n.sub.11                                                   ______________________________________                                    

The compensation pulses (compensation value n) can be changed by lensdesigning. In addition, the compensation pulses are also changeddepending on which of n₁ to n₁₁ the standard value 0 is based. When theprocess advances from step S-R2 to step S-R3, it computes a value AFCR,subtracting the compensation value PEND from the compensation valuePSTRT so as to observe how much the compensation value PSTRT, at whichthe zooming lens group is driven, deviates from the compensation valuePEND at which the zooming lens group is stopped. The process thenadvances to step S-R4 to determine whether the result of the subtractionis 0. When the result is 0, the subject is focused, the determinedcondition is YES and the process advances to step S-R15. When the resultis not 0, the subject is not focused, and the process advances to stepS-R5. The process sets flag SWREN (representing whether the releaseoperation is permitted) to 1 in step S-R15. The process advances to stepS-R16, turns ON the in-focus indication and advances to a step followingthe power zoom drive check process.

When the process determines that the result of the subtraction is not 0in step S-R4 and it has advanced to step S-R5, the process replaces theamount of driving of the focusing lens group, dp, with the absoluteresult of the subtraction of AFCR, in step S-R5. In this case, since theamount of driving is an absolute value, assuming that dp=.linevertsplit.AFCR.linevert split., the process advances to step S-R6 todetermine whether the result of the subtraction, AFCR, is positive ornegative. When the result is positive, the determined condition is YESand the process advances to step S-R8. When the result is negative, theprocess advances to step S-R7. Subroutine AFNEARGO, shown in FIG. 36,drives the focusing lens group to the near side in step S-R7, while thesubroutine AFFARGO, shown in FIG. 35, drives the focusing lens group tothe far terminus side in step S-R8. Both subroutines advance to stepS-R9 when they have completed their routine.

The process determines whether the focusing lens group has been drivenfor the amount of driving, dp, in step S-R9. When the focusing lensgroup has not been completely driven, the determined condition is NO andthe process advances to step S-R10. When the determined result is YES,the process advances to step S-R12. In step S-R10, the processdetermines whether the interval of the pulses being outputted from theAF pulser 48 is at least 100 msec. When the pulse interval is less than100 msec, the determined condition is NO and the process returns back tostep S-R9 so as to enter a loop. When the process determines that thepulse interval exceeds 100 msec in step S-R10, the process advances tostep S-R11 to execute the terminus point process subroutine, shown inFIG. 23. The AF drive stop subroutine, shown in FIG. 22, takes placewhen processing goes from step S-R9 to step S-R12. Then, the processadvances to step S-R13.

The process determines whether flag NL (representing whether the nearterminus of the focusing lens group is being detected) has been set to 1in step S-R13. When the determined condition is NO, the process advancesto step S-R14 to determine whether flag FL (representing whether the farterminus of the focusing lens group is being detected) has been setto 1. When the determined condition is NO, the process advances to stepS-R15 to set flag SWREN (representing whether the release operation ispermitted) to 1 before advancing to step S-R16 to turn ON the in-focusindication. Processing then advances to a step following the power zoomdrive check process. When the determined condition either in step S-R13or step S-R14 is YES, steps S-R15 and S-R16 are skipped. Instead,processing advances to a step following the power zoom drive checkprocess.

Lens Sheltering Check

This process determines whether the main switch, namely the lock switchSWLOCK, has been turned ON in step S-LC1, shown in FIG. 32. When theswitch has been turned ON, the determined condition is YES and theprocess advances to a step following the power zoom drive check. Whenthe determined condition is NO, the process prohibits the timerinterrupt (step S-LC2) and then advances to step S-LC3 to execute theAFSTOP subroutine, shown in FIG. 41, so as to stop the focusing lensgroup. In step S-LC4, the ZOOMSTOP subroutine, shown in FIG. 42, takesplace to stop the zooming lens group. Thereafter, the process determineswhether the AF mode switch (switch SWAF A/M) has been turned ON in stepS-LC5. When the switch has been turned ON, namely the AF mode takesplace, the determined condition is YES and the process advances to stepS-LC6. When the determined condition is NO (manual), the processadvances to step S-LC14. The process determines whether the focusinglens group is of a shelter type in accordance with the informationstored in the lens ROM 43 in step S-LC6. When the focusing lens group isof the shelter type, the determined condition is YES and the processadvances to step S-LC7. When the determined condition is NO, the processadvances to step S-LC14.

The process determines whether the power zoom switch SWPZ has beenturned ON in step S-LC14. When the switch has been turned ON, thedetermined condition is YES and the process advances to step S-LC15. Theprocess determines whether the zooming lens group is of the shelter typein accordance with the information stored in the lens ROM 43 in stepS-LC15. When the zooming lens group is of the shelter type , thedetermined condition is YES and the process advances to step S-LC11.When the process determines that the power zoom switch SWPZ has beenturned OFF in step S-LC14 or that the zooming lens group is not of theshelter type in step S-LC15, the determined condition is NO and theprocess advances to step S-U18. This cancels the power hold operation.

When the process advances from step S-LC6 to step S-LC7, it drives thefocusing lens group in a direction where it can be retreated in stepS-LC7 and advances in step S-LC8. The process then sets flag AFGO(representing whether the focusing lens group is being driven) to 1 instep S-LC8. The process then determines whether the power zoom switchSWPZ has been turned ON in step S-LC9. When the switch has been turnedON, the determined condition is YES and the process advances to stepS-LC10 to determine whether the zooming lens group is of the sheltertype, in accordance with the information stored in the lens ROM 43. Whenthe zooming lens is of the shelter type, the determined condition is YESand the process advances to step S-LC11 to drive the zooming lens groupin a direction where it is retreated in step S-LC11. In step S-LC12,flag PZGO (representing whether the zooming lens group is being driven)is set to 1 before the process advances to step S-LC13.

When the process determines that the power zoom switch SWPZ has beenturned OFF in step S-LC9 or that the zooming lens group is not of theshelter type in step S-LC10, the determined condition is NO and theprocess advances to step S-LC13. When the process advances from stepS-LC12, step S-LC9 or step S-LC10 to step S-LC13, the process activatesa sheltering timer for the lens, the value of which has been stored inthe lens ROM 43, and then advances to step S-U1 in FIG. 33.

In step S-U1, the process determines whether flag AFGO (representingwhether the focusing lens group is being driven) has been set to 1(drive state). When the focusing lens group is being driven, thedetermined condition is NO and the process advances to step S-U7. Whenthe focusing lens group is being driven, the determined condition is YESand the process advances to step S-U2. The process determines whetherthe AF mode switch (switch SWAF A/M) has been turned ON in step S-U2.When the switch has been turned ON and the AF mode takes place, thedetermined condition is YES and the process advances to step S-U3. Whenthe determined condition is NO (manual mode), the process advances tostep S-U4. The process determines whether the interval of the pulsesbeing outputted from the AF pulser 48 is at least 100 msec in step S-U3.When the pulse interval is less than 100 msec, the determined conditionis NO and the process advances to step S-U5. When the pulse interval is100 msec or more, the determined condition is-YES and the processadvances to step S-U4.

When the process advances from step S-U3 to step S-U5, it counts thepulse count value AFP, which is the number of pulses being outputtedfrom the AF pulser 48 and then advances to step S-U6 to determinewhether the pulse count value AFP is smaller than the maximum value ofdriving the focusing lens group, AFPmax. When the pulse count value AFPis smaller than AFPmax, the determined condition is YES and the processadvances to step S-U7. When AFP is larger than AFPmax, the determinedcondition is NO and the process advances to execute the AFSTOPsubroutine, shown in FIG. 41, to stop the focusing lens group, because,if the pulses which are, outputted from the AF pulser 48 arecontinuously outputted, even if they exceed AFPmax, the battery powerwould be quickly consumed. Thus, it is necessary to stop the focusinglens group.

Next, the process determines whether flag PZGO (representing whether thezooming lens group is being driven) has been set to 1 (drive state) instep S-U7. When the zooming lens group is not being driven, thedetermined condition is NO and the process advances to step S-U13. Whenthe zooming lens group is being driven, the determined condition is YESand the process advances to step S-U8. The process then determineswhether the zooming switch SWPZ has been turned ON in step S-U8. Whenthe switch has been turned ON, the determined condition is YES and theprocess advances to step S-U9. When the determined condition is NO, theprocess advances to step S-U10. In step S-U9, the process determineswhether the interval of the pulses being outputted from the PZ pulser 49is at least 100 msec. When the pulse interval is less than 100 msec, thedetermined condition is NO and the process advances to step S-U11. Whenthe interval exceeds 100 msec, the process advances to step S-U10.

When the process advances from step S-U9 to S-U11, it counts a pulsecount value, PZP, of pulses being outputted from the PZ pulser 49 andthen advances to step S-U12 to determine whether the pulse count valuePZP is larger than the maximum value for driving the zooming lens group,PZPmax. When PZP is smaller than PZPmax, the determined condition is YESand the process advances to step S-U13. When PZP is larger than PZPmax,the determined condition is NO and the process advances to step S-U10 toexecute a ZOOMSTOP subroutine, shown in FIG. 42, to stop the zoominglens group, before advancing to step S-U13, because, if the pulses whichare outputted from the PZ pulser 49 are continuously outputted, even ifthey exceed PZPmax, battery power would be quickly consumed. Thus, it isnecessary to stop the focusing lens group.

In step S-U13, a determination is made as to whether flag AFGO(representing whether the focusing lens group is being driven) has beenset to 1. When the focusing lens group is not being driven, thedetermined condition is NO and the process advances to step S-U14 todetermine whether flag PZGO (representing whether the zooming lens groupis being driven) has been set to 1. When the zooming lens group is notbeing driven, the determined condition is NO and the process advances tostep S-U18 to cancel the power hold. Processing is then completed.

When the process determines that the focusing lens group is being drivenin step S-U13, or that the zooming lens group is being driven in stepS-U14, the determined condition is YES and the process advances to stepS-U15 to determine whether the sheltering time period has elapsed. Whenthe sheltering time period has not elapsed, the determined condition isNO and the process advances to step S-U19 to determine whether the mainswitch, namely the lock switch SWLOCK, has been turned ON. When theswitch has been turned OFF, the determined condition is NO and theprocess advances to step S-U1, so as to enter a loop. When the switchhas been turned ON, the determined condition is YES and the processadvances to step S-K1 in FIG. 30.

On the other hand, when the process advances from step S-U15 to stepS-U16, the AFSTOP subroutine, shown in FIG. 41, is executed to stop thefocusing lens group. Thereafter, the ZOOMSTOP subroutine, shown in FIG.42, takes place to stop the zooming lens group. Then, the processcancels the power hold and ends the routine.

In the above embodiment, the zoom position is detected by the zoom codeplate. However, it is obvious that modifications and variations of thepresent invention are possible. For example, as shown in FIG. 43, areflection plate 64, for detecting a position which moves in aperipheral direction is mounted on the outer surface of a cam ring 29. Areflection type photo detector 65 is on an opposite side of thereflection plate 64. The photo detector 65 comprises a light emittingelement (LED) which emits light to the reflection plate 64 and a lightreception element which receives the light reflected from the reflectionplate. In addition to the reflection plate 64, as shown in FIG. 44(A), aconcentration changing type reflection plate, whose concentrationschange from one side to other side, can also be used. As shown in FIG.44(B), a bar code plate type reflection plate can also be used.

As shown in FIGS. 45 and 46, it is also possible to detect a zoomposition by a change of an electrostatic capacity of a variable capacitytype zoom position detection means, which comprises an electrode plate66 fixed to the base of a cam ring 29 and an electrode plate 67 mountedon a fixing frame 27 on an opposite side of the electrode plate 66.

As shown in FIG. 47, a zoom position can be detected by a change of avariable resistor of a variable resistor type zoom position detectionmeans, which comprises a resistor plate 68 that is fixed on the base ofa cam ring 29 in the peripheral direction and a brush 69 which touchesthe resistor plate 68.

FIG. 48 conceptually shows the relationship between the power zoommechanism and the pulser. In the first embodiment, the zoom code plateand PZ pulser are commonly used. However, it is possible to provideanother zoom code plate along with such a pulser. On the other hand,another pulser substituted for the zoom code plate can be used alongwith the PZ pulser.

In FIG. 48, a gear 70 is provided on the base of a cam ring 29. The gear70 is linked with PZ motor M2 through a speed reduction gear mechanism71. The speed reduction gear mechanism 71 comprises a gear 72 which isengaged to the gear 70, a pinion 73 which is engaged with the gear 72,an idle shaft 74 with which the pinion 73 is engaged, and a gear 75fixed to the idle shaft 74. A transparent type PZ pulser 49 is providedbetween the idle shaft 74 and a barrel, not shown. The PZ pulser 49comprises a slit plate 76 fixed to the idle shaft 74 and a photodetector 77 positioned on a peripheral side of the slit plate 76. Asshown in FIG. 49, the peripheral portion of the slit plate 76 has manyslits 76a therein in which the pitches radiate in radius directions. Thephoto detector 77 is positioned in the manner that the peripheralportion of the slit plate 76 is surrounded by a light emission element77a and a light reception element 77b. PZ motor M2 and the speedreduction gear mechanism 71 are not limited to the positions shown inthe diagram. The positions can be changed considering other parts.

It is also possible to use a reflection type PZ pulser 49 besides thetransparent type. FIGS. 50 and 51 show an example of a reflection typepulser. In this example, a reflection plate 78 is fixed to the idleshaft 74. Many reflection planes 78a, which extend in the radiusdirections of the reflection plate 78, are provided thereon. Areflection type photo detector 79, which functions like the photodetector 52, is on an opposite side of the reflection plate 78.

FIGS. 52 and 53 show another example of a reflection type pulser. Inthis example, a multiple side reflector 80, whose peripheral portionreflects light, is fixed to the idle shaft 74. On a peripheral plane ofthe multiple side reflector 80, a reflection type photo reflector 81,which functions like the photo detector 52, is positioned.

The means for selecting the image magnification constant value desiredby the camera operator can be set in a number of ways. Numerousembodiments, not discussed herein, can be designed that accomplish thedesired task of selecting a desired magnification value. The followingembodiments are illustrative only and do not limit the scope of theinvention. For example, a plurality of switches can be provided on thecamera body, the camera lens, or both, to select one of a plurality ofpresent magnification values. A second type of magnification valuesetting means can comprise an up/down switch that selects a particularmagnification value. Alternatively, a single pushbutton switch can beemployed that cycles through a predetermined number of magnificationvalues.

Instead of limiting the magnification values to a limited number ofsettings, the magnification setting means can be designed to allow theselection of one magnification value from an infinite number ofmagnification values. Furthermore, a range of magnification values canbe provided from which a magnification value is selected. Such a rangecan be based upon the type of lens attached to the camera body.

While the present embodiment of the invention describes prohibiting therelease of the shutter unt11 an image returns to an allowed range duringan image magnification constant operation, other procedures can bedeveloped without departing from the scope and intent of the presentinvention. For instance, a software program can be written, such thatwhen a subject leaves an area wherein an image magnification constantoperation can be performed, the image magnification constant operationis terminated, while the automatic focus operation of the cameracontinues to operate so that a photograph can be taken. Alternatively,the camera can be programmed to give either a visual, audible or visualand audible indication when the object to be photographed is no longerwithin the range of the camera's lens for the image magnificationconstant operation to correctly operate. Alternatively, the camera canbe programmed such that when the object to be photographed leaves theimage magnification constant range, the shutter release on the camera isinhibited unt11 the object re-enters the range of the camera lens inwhich the image magnification constant operation can function.Furthermore, the auto-focus operation can be programmed to continueoperating during this time so that the camera is prepared to take aphotograph as soon as the object to be photographed returns to the rangein which the image magnification constant operation is functional.

Various other procedures and variations of the above-describedprocedures are possible by preparing an appropriate software programthat is executed by the camera microprocessor. It is even possible tocreate a software program embodying more than one procedure so that thecamera body can choose a procedure based upon the lens and/or situationthat exists at the time a picture is taken.

FIGS. 15(a) and 17(a) show a modified embodiment of the invention. Inthis modification, when a subject is moved out of a range where theimage magnification can be controlled, the image magnification controlcan be temporarily stopped. When the subject moves back into theallowable range of the image magnification control, the imagemagnification control is resumed.

More particularly, as illustrated in FIG. 15(a), after step S-B10 isexecuted (which is the same as in FIG. 15), a control imagemagnification ##EQU5## is computed at step S-B120. Thereafter,processing returns to step S-B1 via steps S-B13 through S-B17. If thedetermined condition at step S-D14 (FIG. 17(a)) is NO, processing goesto step S-D30.

When the process advances to step S-D30, it determines whether theinterval of the pulses being output from the PZ pulser 49 is at least100 msec. When the determined condition is NO (less than 100 msec), theprocess advances to step S-D1 in FIG. 17(a) to enter a loop until thedetermined condition becomes YES. When the determined condition is YES,the process advances to step S-D31 to stop driving the zooming lensgroup. Thereafter, processing advances to step S-D32 to determinewhether the direction of the zooming lens group is being driven towardsthe tele terminus. When the determined condition is YES, the processadvances to step S-D33. When the determined condition is NO, the processadvances to step S-D34. The process sets flag TL (representing whetherthe tele terminus of the zooming lens group is being detected) to 1 instep S-D33 and then returns back to step S-B1, shown in FIG. 15(a). Theprocess sets flag WL (representing whether the wide terminus of thezooming lens group is being detected) to 1 in step S-D34 and thenreturns back to step S-B1 in FIG. 15(a).

Moreover, as in FIG. 17, the process determines whether the zooming lensgroup has been driven for Pz in step S-D8. When the determined conditionis YES, the process advances to step S-D9. When the determined conditionis NO, the process advances to step S-D35 to determine whether theinterval of pulses being output from the PZ pulser 49 is at least 100msec. When the determined condition is NO, the process returns back tostep S-D8, so as to enter a loop until the zooming lens group has beendriven for Pz. When the determined condition is YES, the processadvances to step S-D36.

When the process advances to step S-D36, it stops driving the zoominglens group. After that, the process advances to step S-D37 to determinewhether the zooming lens group is being driven towards the teleterminus. When the determined condition is YES, the process advances tostep S-D38. When the determined condition is NO, the process advances tostep S-D39. The process sets flag TL (representing whether the teleterminus of the zooming lens group is being detected) to 1 in step S-D39and sets flag WL (representing whether the wide terminus of the zoominglens group is being detected) to 1 in step S-D38. After that, theprocess advances to step S-D10. The terminus point process takes placein step S-D10 and then processing returns back to step S-B1 in FIG.15(a).

FIGS. 3(a), 14(a) and 15(b) show another modified embodiment of theinvention. In this modification, the image magnification can beexternally set.

More particularly, as illustrated in FIG. 3(a), an image magnificationexternal setting switch SWIMG is employed which is connected to terminalP28 of the lens CPU 44. By turning ON the switch, a desired imagemagnification can be input from an image magnification external settingcircuit 60'. The desired magnification being input from the imagemagnification external setting circuit 60' can be gradually or stepwiseinput. Switches SWPZC and SWIMG can be also provided on the body.

In this connection, as illustrated in FIG. 14(a), after step S5 isexecuted, it is determined whether the external image magnificationsetting mode is set at step S5', before advancing to step S6. If theanswer is YES, the process goes to step S25, instead to S6.

Further, steps S-B3 and S-B3A in FIG. 15(b) are executed. In step S-B3A,the process determines whether the image magnification external settingmeans SWIMG has been turned ON. When the switch has been turned ON, thedetermined condition is YES and the process advances to step S-B3B. Whenthe switch has not been turned ON, the determined condition is NO andthe process advances to step S-B4 in FIG. 15(b). In step S-B3B, theprocess inputs the desired image magnification being set by switch SWIMGand then advances to step S-B6 in FIG. 15(b).

What is claimed is:
 1. An image magnification control device for acamera having a photographic lens, comprising:distance detecting meansfor detecting a distance "X0" between a rear focal point of saidphotographic lens and an image taking plane of said camera; defocusdetecting means for detecting a defocusing amount "dx" corresponding toa distance between said image taking plane and a surface on which animage is formed by said photographic lens; first calculating means forcalculating a magnification ratio γ of a control focal length "f1"required to maintain an image magnification to a present focal length"f0", based on said distance "X0" and said defocus amount "dx" inaccordance with an equation: ##EQU6## second calculating means forcalculating a driving amount of said photographic lens to maintain saidimage magnification, based on said magnification ratio γ; and means fordriving said photographic lens, based on said driving amount calculatedby said second calculating means, to change a focal length of saidphotographic lens.
 2. The device of claim 1, wherein said distancedetecting means detects said distance "X0" based on a focus position anda zoom position of said photographic lens.
 3. The device of claim 1,wherein said second calculating means calculates said driving amountbased on said magnification ratio "γ" using coefficients that changeaccording to a zoom position of said photographic lens.
 4. The device ofclaim 1, wherein said driving means stops driving said photographic lenswhen said photographic lens reaches one of a tele terminus and a wideterminus.
 5. An image magnification control device for a camera having aphotographic lens, comprising:a distance detector that detects adistance "X0" between a rear focal point of said photographic lens andan image taking plane of said camera; a defocus detector that detects adefocusing amount "dx" corresponding to a distance between said imagetaking plane and a surface on which an image is formed by saidphotographic lens; an image magnification calculating system thatcalculates a magnification ratio γ of a control focal length "f1"required to maintain an image magnification, to a present focal length"f0", based on said distance "X0" and said defocus amount "dx" inaccordance with an equation: ##EQU7## a driving amount calculator thatcalculates a driving amount of said photographic lens to maintain saidimage magnification, based on said magnification ratio γ; and a lensdriver that drives said photographic lens, based on said driving amountcalculated by said driving amount calculator, to change a focal lengthof said photographic lens.
 6. The device of claim 5, wherein saiddriving amount calculator calculates said driving amount based on saidmagnification ratio "γ" using coefficients that change according to azoom position of said photographic lens.
 7. The device of claim 5,wherein said lens driver stops driving said photographic lens when saidphotographic lens reaches one of a tele terminus and a wide terminus. 8.The device of claim 5, wherein said driving amount calculator calculatessaid driving amount based upon said magnification ratio "γ", accordingto an equation:

    Aγ.sup.3 +Bγ.sup.2 +Cγ,

wherein A, B and C represent coefficients that change according to azoom position of said photographic lens.
 9. The device of claim 5,wherein said distance detector detects said distance "X0" based on afocus position and a zoom position of said photographic lens.
 10. Amethod for controlling an image magnification of a camera having aphotographic lens, comprising the steps of:detecting a distance "X0"between a rear focal point of the lens and an image taking plane of thecamera; detecting a defocusing amount "dx" corresponding to a distancebetween the image taking plane and a surface on which an image is formedby the lens; calculating a magnification ratio γ of a control focallength "f1" required to maintain an image magnification, to a presentfocal length "f0", based on the detected distance "X0" and the detecteddefocus amount "dx" in accordance with an equation: ##EQU8## calculatingan amount to drive the lens to maintain the image magnification, basedon the magnification ratio γ; and driving the lens, based on thecalculated drive amount, to change a focal length of the lens.
 11. Themethod of claim 10, wherein the distance detecting step comprises thestep of detecting the distance "X0" based on a focus position and a zoomposition of the lens.
 12. The method of claim 10, wherein the driveamount calculating step comprises the step of calculating the drivingamount based on the magnification ratio "γ" using coefficients thatchange according to a zoom position of the lens.
 13. The method of claim10, further comprising the step of stopping the driving of the lens whenthe lens reaches one of a tele terminus and a wide terminus.
 14. Themethod of claim 10, wherein the drive amount calculating step comprisesthe step of calculating the driving amount based upon the magnificationratio "γ", according to an equation:

    Aγ.sup.3 +Bγ.sup.2 +Cγ,

wherein A, B and C represent coefficients that change according to azoom position of the lens.